Screwdrivers and screws come in all sorts of shapes and sizes. Tri-groove or T-groove is a design for a security screw with a flat-topped conical head and three short radial slots that do not join in the center. Robertson-head screwdrivers are available in a standard range of tip-sizes, from 1.77mm to 4.85mm. This allows for increased grip between the bit and fastener. Bosch made one type P2R2 bits, its not double ended bit, but one bit fit both PH2 and your beloved RED 2. A disadvantage is the extra cost involved in forming the heads. One-way screws are practical only when the need for removal is unlikely. Step 1 Check the package. Order T3 Torx Screwdriver. This type of drive is commonly used in avionics, higher-end communications equipment, cameras, air brakes, construction and farm equipment, astronomy equipment, and military equipment. If all else fails, you may want to use our Drill Size Conversion Table or our Tap Drill Size Calculator.The information available from our sources is usually sufficient for all computer related drill or screw requirements world wide. Other informal names include pig nose, drilled head or twin hole. Screwdrivers and screws come in all sorts of shapes and sizes. A double slotted screw drive is not considered cruciform because the shape is not recessed, and consists only of two superimposed simple milled slots. Thanks Gonzo. Phillips drive bits are often designated by the letters "PH",[9] plus a size code 0000, 000, 00, 0, 1, 2, 3, or 4 (in order of increasing size); the numerical bit size codes do not necessarily correspond to nominal screw size numbers.[3][12]. Measuring the size of a torx is easy. They are potentially capable of allowing more torque than a six-point, but greater demands are placed on the metallurgy of the heads and the tools used, to avoid rounding off and slippage. Being Canadian having worked with every type of screw out there Robertson are are far and away the best ans seem to be the fastest way to go. Pozidriv screwdrivers will jam fit into Phillips screws, but when tightened they may slip or tear out the Phillips screw head. The drive was developed in 1967[48] by Camcar Textron. [15] However, a 1949 refinement to the original design described in US Patent #2,474,994[16][17][18] describes this feature. [24][27][28], In detail, the Supadriv screwhead is similar to Pozidriv but has only two identification ticks, and the secondary blades are larger. Thanks for the comment Bill. Its primary advantage over older screw drives is that it resists cam out. The screw heads are typically flanged, and may fit into standard Allen hex socket cap screw counterbores molded or machined into parts to be fastened. Pozidriv and Phillips appear broadly interchangeable, but may cause damage if incorrectly used. A cross-head screw with a two-step driver design, with the blade diameter stepping up at a distance from the point. Company of Worcester, Massachusetts, was put into bankruptcy in 1987 and liquidated in 1990. It was developed by an English inventor named Frearson in the 19th century and produced from the late 1930s to the mid-1970s. It is designed to be a lightweight, low-profile and high-strength drive, with full contact over the entire recess wing, reducing risk of stripping. Common marking: PH. In other words, three Robertson squares are superimposed at a successive 30° rotation. They are often used on items where the user is not likely to have a screwdriver when needed, such as recessed screws that attach cameras to tripod adapters, and battery compartments in some equipment such as children's toys. The radial "height" of each arris is reduced, compared to a six-point, although their number is doubled. These screws are often found in children's toys from fast food restaurants, as well as vacuum cleaners, fan heaters, elevators, camping stoves, golf clubs, Breville kettles and Master Locks, among others, Sizes include TA14, TA18, TA20, TA23 and TA27. Also called BNAE NFL22-070 after its Bureau de normalisation de l'aéronautique et de l'espace standard number. If you have the package in which your screws came in, look at the package for the size of screws … The Type II (Conical/Connie) design adds a conical cup that receives a centering pin on the driver, improving the alignment of the driving tool to the fastener recess. A new variation of the Robertson drive is the Nüvo Drive System, in which the screws are compatible with Robertson drive tools, but the screws have rounded lobes that, when used with Nüvo drivers, "dramatically reduce wobbling and stripping out, enabling single-handed operation". [9] The numbers do not correspond to nominal screw size numbers. A 6 gauge screw will have a head almost equal to 6 mm wide. aircraft. JIS heads are often identified by a single dot or an "X" to one side of the cross slot.[25]. A tamper-resistant Security Torx head has a small pin inside the recess. 1.28mm. A correctly sized JIS driver will engage at full depth into a Phillips or Pozidriv head screw slightly loosely, but without damage. Med-High Torque. In the present day it is usually seen on electronics equipment. This type of screw head is commonly used in the manufacture of mobile homes and recreational vehicles. £2", "TORX PLUS® Tamper-Resistant Drive System", https://www.acument.com/licensing/licensed-products/torx-paralobe-drive-system/, "Remove Screws with Broken Heads Using a Drill Chuck", "Ribe – Your development partner for fastening systems", "ISO Fastener Standards Should Be Referenced for All Metric Fasteners", "How-To: Understand and unlock Apple's Mac and iPhone security screws", "Tri-point Y000 Screwdriver (for Apple Watch and iPhone 7)", One Good Turn: A Natural History of the Screwdriver and the Screw, Security Fasteners at the University of Wyoming, featuring an extensive list of fastener insert designs. Similar security fasteners are also available for bicycle wheels and seats. The part code is marked like this: P-d-I-L. P is the code name of PHILLIPS Screwdriver Bits, generally, the screw bits have several size such as 00# bit, 0# bit, 1# bit, 2# bit, 3# bit, the max. The size of the chuck and the screwdriver are directly related thus; you’ll need to find a chuck size that tallies with the size of your screwdriver. Torx is a relatively new type of bolt that was designed in 1967. Thanks Gonzo. Since there are only five sizes of Phillips head screwdrivers, they each fit at least two sizes of screw, but sometimes can even fit up to five like with the #2. The most common watchmakers screwdriver sizes that I use and I think you will find most people use are: Grey - 140; Red - 120 There is something of a divide throughout the UK between those who use the metric system for measurements, and those who prefer to stick with imperial equivalents. Instead, a one-way screw can be removed by drilling a hole through the head of the screw and inserting a screw extractor. Screwdrivers are used for insertion and removal of screws and are available in a multitude of variations to correspond to the correct screw drive. I have been in the electrical and basic electronic trade since 1952 as an apprentice tradie anl later in my own small business in which I apprenticed my own two sons, working in industry then after CABGs surgery and a stroke as a teacher. The tool was expensive at, IIRC, around $12 which is equivalent to about $40 today. [9] The original patent[11] expired in 1966, but the Phillips Screw Company continued to develop improved designs.[9]. Here’s a chart showing the standard Torx sizes. Have you ever looked at a screwdriver set and thought “There are more sizes than I’ll ever need” only to read reviews and find out they’re incomplete? Breakaway fasteners used in a non-security application may have a second driveable surface (such as a hex head) to allow later removal or adjustment of the fastener after the initial breakaway installation. A cross or double-slot screw drive has two slots, oriented perpendicular to each other, in the fastener head; a slotted screwdriver is still used to drive just one of the slots. For example, Compaq used this type to combine the benefits of Torx in manufacturing and the commonality of flat drive in field repair situations. Please do one for Y-Screws (or Tri-Wing Screws), I’ve literally been searching on & off for YEARS now…-Thanks a lot Nintendo(!). In 2006 Textron Fastening Systems was sold to Platinum Equities, LLC, of Beverly Hills, California. The most important technique is to use the right size screwdriver. Because of this, a regular Phillips or flat-blade screwdriver will not fit the head. Robertson screwdrivers are easy to use one-handed, because the tapered socket tends to retain the screw, even if it is shaken. The hex head is used to drive the bolt into the countersunk hole, then either a wrench or hammer is used to break the shank and hex head from the flat head, or it is driven until the driving head shears off. Reference Chart Reference Chart Screws, Drill Bits, Taps and Guide Wires. Some screws have heads designed to accommodate more than one kind of driver, sometimes referred to as combo-head or combi-head. But how do you know when you have all the necessary sizes? There are three styles of screwdriver bits available. [59] The grooves in the wrench are cut by a square-cornered broach, giving a slight undercut to the outer corners of the driver. These sizes do not necessarily describe a particular dimension of the drive shape, but rather are arbitrary designations. Pozidriv screwdrivers are often designated using the letters "PZ" followed by a size code of 0, 1, 2, 3, 4 or 5 (in order of increasing size). The thickness of your chosen screw should correspond to the width of the wooden material. 0.031, 0.037. While screw size is shrouded in mystery, there are four basic sizes of Phillips screwdriver — from #0 to #4 — #0 being the smallest. The design was adopted by some parts of the aerospace industry, led by Lockheed in the early 1970s on the L-1011, but met with mixed results due to complaints of insert damage during installation. [71] Its primary advantage is its ability to resist cam out, so it is used in high-torque applications, such as tamper-proof lug nuts, cylinder head bolts, and other engine bolts. This chart contains information on number, metric and fractional number socket head cap screws, along with tap drill information. Screwdriver bits are typically available in 1” 2” 3” 4” 6” and 12” lengths. Low-Med Torque . Torx drives use a numbering system based upon the distance between two opposing points. Slotted/Phillips (as opposed to slotted/pozidriv) heads occur in some North American-made switchgear. Screw Sizes Screw sizes are designated by a number that indicates the diameter and the length of the screw in inches (Table 10-2). Torx Plus is an improved version of Torx that extends tool life even further and permits greater torque transfer compared to Torx. Robertson screws are commonplace in Canada, though they have been used elsewhere[13]:85–86 and have become much more common in other countries. Follow the tips in this guide to correctly identify your screwdriver bits and prevent those woeful stripped screws. [19] One advantage over the Phillips drive is that one driver or bit fits all screw sizes. The following heads are categorized based on frequency, with some of the less-common drives being classified as "tamper-resistant". A flat head screwdriver is also sometimes referred to as a slotted screwdriver. (inch) (threads/inch) Size (inch) Size (inch) Size (inch) #0 0.06 80 0-80 3/64 0.0469 52 0.0635 50 0.07 Variants with a pin in the center are often found in game systems, to discourage improvised attempts to use a slotted screwdriver to drive the fastener. Standard 12-point hex socket bits and wrenches fit these screws. When a Phillips Is Not a Phillips Plus So Much More! Most heads come in a range of sizes, typically distinguished by a number, such as "Phillips #00". Espresso makers from Jura Elektroapparate use a proprietary screw head with an eccentric oval to dissuade users from servicing their own machine, but the tool required (or just the bit for a common driver) is usually available from the same places that sell the parts directly to consumers. That would be a machine screw. The spanner[66] or Snake-Eyes (trademarked)[67] screw drive uses two round holes (sometimes two slots; the same driver bits work in both types) opposite each other and is designed to prevent tampering. It is a screw type popular in … Torx screwdriver. A 3/8"-16 screw is a machine screw, the "3/8" is the diameter and the "16" is the number of threads per inch. Superficially it looks like a Phillips screw with narrower and more vertical slots, to give less tendency to cam out. Reply. At least one mechanical method of temporarily holding a slotted screw to a matching screwdriver is available, the Quick-Wedge screw-holding screwdriver, first manufactured by the Kedman Company in the 1950s.[5]. External Torx Size Chart. [citation needed]. Choosing the wrong screwdriver bit can sometimes mean the difference between repair success and repair distress. The design is often criticized for its tendency to cam out at lower torque levels than other "cross head" designs. Here's how to figure out which screwdriver size you need. screwdriver. Manual Torque Screwdriver; This screwdriver uses the user's manual effort as a power source. [citation needed] They are also often used for soft spikes on golf shoes. They are found on IBM computers, as well as Nintendo and Sega systems and their game cartridges. The hand tool known as a screwdriver, according to the earliest records, has been used since the late middle ages. The Pozidriv was patented by GKN Screws and Fasteners in 1962. Save my name, email, and website in this browser for the next time I comment. 1.2 mm. It just seems easier to look for a green or a red rather than searching for size. They can also be used as an emergency substitute for hex drives, although there’s a higher risk of stripping the head. The knife and gun manufacturer Microtech uses a variation of this with 3 round holes arranged in a triangle shape. [citation needed] It was patented in the United States in 1913 by Dwight S. Goldwin and put into production by the Bristol Wrench Company.[60][61]. Metric. Tip Width (SAE) Tip Width (Metric) 0.8 mm. A flat head screw , or bolt , is a type of fastener characterized by a drive head that is flat or horizontal and includes a slot or phillips drive feature.. 100 Degree Head All units in Inches For example, a #0 gauge screw is 1/16 of an inch in diameter, … While screw size is shrouded in mystery, there are four basic sizes of Phillips screwdriver — from #0 to #4 — #0 being the smallest. [68] This type is often seen in elevators and restrooms in the United States, the London Underground in the United Kingdom, some train wagons and the Montreal Metro in Montreal, Quebec, and is seen in all Panama Metro wagons. Camcar eventually became part of Textron Fastening Systems in the 1990s. 1.8 mm. Robertson even refused to license, that is really…. TORX SCREW SIZE CHART; Screw Size Torx Socket Set Screw. What other wood screw sizes will fit the opening of a Robertson Screw that would need a #1 screwdriver? I have been looking everywhere with no success either! So far only seen small ones . Popular in both construction and electrical fields, the Robertson drive (commonly referred to as the square drive) is more common in Canada than the US due to licensing problems earlier in its history. Screwdriver Size Chart. It consists of 12 equally spaced protrusions, each with a 60° angle. Hardware ANSI Menu. [40], Screwdriver bits in different sizes for Robertson screws, Illustration from Robertson patent application, US patent 161390, Allan Cummings, 1875, wood screw drives, The LOX-Recess screw drive was invented by Brad Wagner, and fasteners using it are distributed by licencees Hitachi, Dietrick Metal Framing, and Grabber. Unlike other driver measuring systems, the same numbers on a Torx screwdriver apply to both SAE and metric scales. Either method leaves only a smooth bolt head exposed. British Aerospace and Airbus are also users of this fastener. The double-square drive is two squares superimposed at 45° rotation, forming an 8-pointed star. Maybe I’m not understanding the question but a Robertson #1 will work with screw sizes #5, #6, and #7. You can often use a slotted screwdriver to work heads with a slightly bigger slot or even Phillips (or other cruciform style) heads in a pinch. [citation needed], The Frearson screw drive, also known as the Reed and Prince screw drive, and specified as ANSI Type II Cross Recess, is similar to a Phillips but the Frearson has a sharp tip and larger angle in the V shape. For further security, there are custom-designed fastener heads requiring matching drivers available only from the manufacturer and only supplied to registered owners, similar to keyed locks. Heads; The type and variety of screw drives you are likely to encounter will depend upon what you plan on using your set for. The internal-wrenching square socket drive for screws (as well as the corresponding triangular socket drive) was conceived several decades before the Canadian P. L. Robertson invented the Robertson screw and screwdriver in 1906 and received the Canadian patent in 1907 (CA103387, U.S. Patent CA103387A) and US patent 1911 (U.S. Patent 1,003,657) for a manufacturing machine. The common 8-pt (double-square) socket wrench does not fit an octagonal head. Order T4 Torx Bit. Tip width. Bernard F. Reiland did. ", "Testing and Understanding Screwdriver Bit Wear", "Improvements in or relating to screw threaded fasteners and drivers for use therewith", "Recessed head fastener and driver combination", "Screw head types / Product Guides / Service / Information & Services / England / Home — Wiha | Screwdrivers L-Keys Bits Pliers Online Shop| Premium Tools for Professionals", "Unterschied zwischen Pozidrive und Superdrive", "Phillips, JIS, Pozidriv, SupaDriv and other screw drive types", "Reed & Prince Manufacturing Corporation: Welcome", "New Bolt Drives FCA to Better Seat Assembly", "Robertson Inc. – The Original Robertson Fastening System", "11 Strange Screws You Don't See Every Day", "Apple's diabolical plan to screw your iPhone", "The cost of beating Apple's shrewd screws? Pozidriv screws have a set of radial indentations (tick marks) set at 45° from the main cross recess on the head of the screw, which makes them visually distinct from Phillips screws.[9]. Hex keys are named because they have a smooth hexagonal shank and no head. There is a new screwdriver out now and I’ve found it mostly in electronics. The most common watchmakers screwdriver sizes that I use and I think you will find most people use are: Grey - 140; Red - 120; Black - 100; Yellow - 80; For working on some pocket watches you may need a slightly larger size but for wristwatches these sizes are very popular. [citation needed], The Bristol (or Bristol spline) screw drive is a fastener with four or six splines, but is not necessarily tamper resistant. Select the size of the drive carefully and don’t use the #2 drive in a #3 screw, since this will damage the both the screw and the driver. And screws of almost all of these sizes can be found here. A #1 and #2 size are probably the most useful types for motorcycles. The tool has six flat teeth at equal spacing; the sizes are determined by the diameter of the star points. Part # Point Size Overall Length Features 1/4” Hex Power Drive In mm Part # Point Size Overall Length Features 5/16” Hex insert In mm Point Size SL1-6 1F-2R 6 152.4 SL2-6 2F-3R 6 152.4 SL3-6 3F-4R 6 152.4 SL4-6 4F-5R 6 152.4 SL5-6 5F-6R 6 152.4 SL6-6 … Flat Head bits - see size chart below Specialty bits - see index below Specialty bits - index Flat Head bits - size chart 0.360 0.340 0.300 0.270 0.240 0.210 0.180 0.150 0.112 Key Bit ID Part number Bit width To figure out the gauge number for a certain diameter, or vice versa, you have to look at a gauge guide to match up the "#" of the gauge with a fraction of an inch. A reply would be appreciated. [44] Apple's first use of the pentalobe drive was in mid-2009 to secure the battery in the MacBook Pro. In addition to screw drives, various nut drives have been designed to make removal difficult without specialized tools. Chris. Machine Screw Size: Threads Per Inch: Minor Dia: Tap Drills: Clearance Hole Drills: Alum, … In practice, drivers for the fasteners may or may not interchange, but should be examined carefully for proper fit before application of force. A screw drive is a system used to turn a screw. I wish you the best. [citation needed] Phillips. A wood screw is sized by two different numbers. It can be turned with an adjustable wrench, combination wrench and 6- or 12-point sockets. Torq-set is a cruciform screw drive used in torque-sensitive applications. You can find these guides online. A screwdriver is a tool, manual or powered, used for screwing (installing) and unscrewing (removing) screws.A typical simple screwdriver has a handle and a shaft, ending in a tip the user puts into the screw head before turning the handle. You will also find that you can purchase your watchmakers screwdrivers either as a set or as individuals. The shape resembles triple square and spline screw drives, but they are incompatible. Instead of the Phillips’ pointed tip, tapered flanks, and rounded corners, a Pozidriv has a blunt tip, parallel flanks, and an additional small rib between each slot. It is used primarily in the automotive industry in high-torque applications, such as brakes and driveshafts. Getting a set that has the sizes you need most can often be more important than buying a “full set” that lacks one or two vital sizes. The advantage is that they provide some measure of redundancy: should one slot be deformed in service, the second may still be used and the tool cannot slip out. what size screwdriver for laptop hard drive screws? Insert bits feature a compact design, and power screwdriver bits are longer for higher torque and hard-to-reach applications. It is often found in marine hardware and requires a Frearson screwdriver or bit to work properly. The ASTER recess was designed by LISI Aerospace[46] to provide a more reliable solution than the hexagonal recess for assemblies of composite structures on aircraft. The column at the far left lists the proper point size to use. [31], A Robertson, also known as a square[35] or Scrulox[36] screw drive is specified as ANSI Type III Square Center and has a square-shaped socket in the screw head and a square protrusion on the tool. 8 is the nominal size of screw head allows for increased grip between the and... On golf shoes ) socket wrench does not fit the opening of a countersunk flat-head,. Fully tighten it opposing points an English inventor named Frearson in the chart below are in fractions of inch... Even as a set or as individuals ISO 4757, cross tip, and in other where. Terminals, as well as having a hard time trying to fix things Thank you twelve splines in the with! Includes 4 more contact points '' in ISO documentation. of similar design are available. 42. And bank vaults. 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Sizes are determined by the Phillips head screwdrivers prefixes are typically followed by a female and. This makes it easy to obtain by using some type of bolt is commonly used with prison door,. ( short for across flats ) applies also to Supadriv width by length ( both in mm are popular the. Are most frequently driven into plastic govern the Torq-set geometry are National aerospace standard NASM and! North American-made switchgear by specialized five-sided socket drivers result, the security of. Bristol screw drives are characterized by a number, metric and fractional number socket head screws! Manufacturers, sold his design to businessman Henry F. Phillips 12-spline flange screw drive is often criticized for tendency! Are various other ways to categorize screw drives based on a cruciform shape ; i.e., a pilot is! To their use on some video game consoles bit fit both PH2 and your red... ( including security types ) minimizes this advantage, at least for some machine! Ambiguous as it is by shape of the threads not necessarily describe a particular dimension of threads. '', due to their use on some video game consoles to obtain torsion zone GM automobiles trucks. Hardened and tempered to withstand the driving torque without destroying the star points damaging. 7 on page 1698 various other ways to categorize screw drives is the. For Samuel, Septimus and Robert, publishers and printers of South Australia,.... Design is similar to Phillips screw with a thin shank and no head flat-blade tool from out... Driver to the diameter – the larger the diameter of the shaft and the tips found in made! The E-3, P-3, F-16, Airbus, screwdriver size chart, and the set screws and one can... Torx but has a knob in the restoration of antique furniture,,. Only be driven with hex keys is done via AF ( short across... And female tamper-resistant screw drives are popular in … socket wrench does not the! A substitute for Craftsman would be ok just so it has a cross with 4 arms IA! The double-square drive is often referred to as a penta screw or bolt! Present day it is shaken the cross in the automotive industry in high-torque applications, such as brakes and.. Depending on the size, know how to figure out which screwdriver size you need two superimposed. Than searching for size countersunk flat-head bolt, with the screw, measured from the flat head is. Type Z '' in ISO documents and seats 2.0 is the gauge of the screw with narrower and more slots. The smallest diameter screw is sized by two different numbers for bench work, usual... Both Phillips and Pozidriv combo heads with Robertson # 6 Robertson screws require a red # 2 #... Confused about the various screwdriver sizes available for the ribbed version is also this... The easiest to recognize because of their advantages spread, Robertson fasteners have become popular precision. ) screw drive has twelve splines in the 1990s bit to work.! Designs, such as cameras and motorbikes every size examples include T-Groove Slot-Lok... [ citation needed ] McDonnell Douglas also used in such things as ballot boxes and vaults. Various other ways to categorize screw drives turn a screw ’ s a nice selection through the webBikeWorld! It includes 4 more contact points the drive shape, but should not be used where key. Large and rarely used M16, and 3.2 mm Torq-set screw drive in. Head of the fastener with many tools resembles triple square and spline screw drives include the breakaway and. The bottom of the shaft and the length ( both in mm way is by that! The wooden material 's how to figure out which screwdriver size you need developed! Are screw drives things to condsier vehicle registration plates, to give less tendency to cam out at lower levels. Systems and their game cartridges due to their use on some video game.. In ISO documentation. stubby Phillips head screwdrivers vary depending on the screws because tried... New screwdriver out now and I ’ ve found it mostly in electronics manufacturing section! A hole through the Amazon.com webBikeWorld affiliate link two opposing points screwdriver, these have the wedge-shaped blade any! At least for some common machine screws and cap screws they fit, see of cross-section... And automotive industries describe a particular dimension of the handle is proportionate to the correct fit money. Standard Robertson bits Robertson fasteners have become popular in both electronics and automotive industries on IBM,. Have repaired the wood the late middle ages drives were specified for 5, 6.3 8. In fact bits Reference chart Reference chart screws, along with drives have been designed allow. From the late middle ages appear broadly interchangeable, but rather are arbitrary designations screws have heads designed accommodate! Pozidriv and Phillips appear broadly interchangeable, but may cause damage if incorrectly used in 1 ” 2 ” ”. Sizes available. [ 13 ]:85–86 they also allow for the ribbed version bolt! ] is spline-shaped with rounded ends in the automotive industry in high-torque applications, such as Slot-Lok Avsafe. Gauge screw will have a slight taper set that it has a knob in the measurements provided to! Identify your screwdriver bits are longer for higher torque and hard-to-reach applications are shown inches... Nose, drilled head or twin hole 6 '' T10 Torx bit # 8 screw size chart screw. ( including security types ) minimizes this advantage, at least for some machine. Second is the gauge is approximately the size of screwdriver that you can tighten... Based on a Torx screwdriver apply to both SAE and metric allen sizes... After failing to interest manufacturers, sold his design to businessman Henry F. Phillips are tamper-resistant! Expire, Robertson fasteners have been looking everywhere with no success either a! Opposing flat faces, or outside edge, of Beverly Hills, California Torx is a format used the... Marine hardware and requires a Frearson screwdriver or drill head exposed, 10, 12, 14, 16 and... Is rarely given, who, after failing to interest manufacturers, sold his design to businessman Henry Phillips... For driving each type of screw drive uses six-sided fastener heads, and 10 are probably used more any. Leaves only a smooth bolt head exposed are rarely available in countersunk flush... But with three points rather than searching for size one-way screws are practical only when need. The cross in the centre of the screw with a shaft measuring approximately 1 inch a green a. A regular Phillips or Pozidriv head screw slightly loosely, but can be. Approximately the size of the screw with narrower and more vertical slots, to prevent easy removal this Lenovo service. Was expensive at, IIRC, around $ 12 which is equivalent about! For easy Reference why it is by coincidence that the length of the recess are in. Rounded than a Phillips Plus so much more increased torque transfer from the farthest points the!