A screw drive is a system used to turn a screw. At a minimum, it
is a set of shaped cavities and protrusions on the screw head that
allows torque to be applied to it. Usually, it also involves a mating
tool, such as a screwdriver, that is used to turn it. The following
heads are categorized based on commonality, with some of the
less-common drives being classified as "tamper-resistant".
Most heads come in a range of sizes, typically distinguished by a
number, such as "Phillips #00" or "
1 Slotted drives
1.1 Slot 1.2 Coin-slot drive 1.3 Hi-Torque 1.4 Dzus 1.5 Cross
2.1 Frearson 2.2 Phillips 2.3 Pozidriv 2.4 Supadriv 2.5 Phillips II 2.6 French recess 2.7 JIS B 1012 2.8 Mortorq
3 Square drives
4 Multiple-square drives
4.1 LOX-Recess 4.2 Double-square 4.3 Triple-square
5 Internal hex drives
5.1 Hex socket 5.2 Double hex
6 Hexalobular sockets
7 Combination drives
7.1 ACR Phillips II Plus 7.2 Phillips/square 7.3 Recex 7.4 Slotted/Torx 7.5 Clutch 7.6 Thumbscrew
8 External drives
8.1 Square 8.2 Hex 8.3 Pentagon 8.4 External Torx 8.5 12-point
9 Tamper-resistant types
9.1 Breakaway head 9.2 Bristol 9.3 Line 9.4 One-way 9.5 Pentalobe 9.6 Polydrive 9.7 Proprietary head 9.8 Security hex 9.9 Security Torx 9.10 Spanner 9.11 12-spline flange 9.12 Torq-set 9.13 TA 9.14 TP3 9.15 Tri-point 9.16 Tri-groove 9.17 Tri-wing
10 Other drive types
11 Alternative categorizations 12 Notes 13 References
14 External links
Slot drive tool and fastener sizes
Blade width Fastener size
3⁄32 in (2.4 mm) 0–1
1⁄8 in (3.2 mm) 2
5⁄32 in (4.0 mm) 3
3⁄16 in (4.8 mm) 4–5
1⁄4 in (6.4 mm) 6–7
5⁄16 in (7.9 mm) 8–10
3⁄8 in (9.5 mm) 12–14
7⁄16 in (11 mm) 16–18
1⁄2 in (13 mm) 18–24
The slot screw drive has a single slot in the fastener head and is driven by a "common blade" or flat-bladed screwdriver. It was the first type of screw drive to be developed, and for centuries it was the simplest and cheapest to make. Uniquely among common drives, it is straightforward to manufacture a slot head or drive by hand. The slotted screw is commonly found in existing products and installations, and is still used in some simple carpentry, and applications where little torque is needed. It is used in restoration of old and antique furniture, vehicles and equipment. However, it is not well suited to installation with power tools, because a power driver tends to slip out of the head, potentially damaging the screw and surrounding material. For this reason, cruciform and other drives have replaced it in most applications. The tool used to drive a slot is called a common blade, flat-blade, slot-head, flat-tip or flat-head / flathead screwdriver. A hollow-ground screwdriver is less likely to "cam out" (leave the slot due to torque being translated into an axial force), so more torque can be applied without damaging the screw head. Flat-blade jewelers' screwdrivers and the tips found in 1⁄4-inch drive sets are generally hollow-ground. Coin-slot drive
Coin-slot drives are so-called because of the curved bottom of the recess that facilitates driving them with a suitable coin, are often used on items where the user is not likely to have a screwdriver when needed, such as on thumb-screws that attach cameras to tripod adapters and battery compartments in some equipment. Hi-Torque
Dzus (pronounced "Zeus") screws are similar to Hi-
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. This type is usually found in cheaply-made roofing bolts and the like, where a thread of 5 mm (0.20 in) or above has a large flattened pan head. The sole advantage is that they provide some measure of redundancy: should one slot be deformed in service, the second may still be used.
The Frearson screw drive, also known as the Reed and Prince screw
drive, and specified as
Phillips drive tool and fastener sizes
Driver size Wood Screw Size
Machine Screw Size
#0 #0–#1 #0 and #1
#1 #2–#4 #2, #3, #4
#2 #5–#9 #5–#10
#3 #10–#16 #12, 1⁄4″, 5⁄16″ if round-head
#4 #18–#24 3⁄8″, 9⁄16″, plus 5⁄16″ if flat-head
The Phillips screw drive (specified as an
Screws with the Pozidriv head.
The Pozidriv (sometimes incorrectly spelled "Pozidrive") is an
improved version of the Phillips screw drive. It is designated "Type
The Supadriv (sometimes spelled incorrectly as "Supadrive") screw drive is very similar in function and appearance to Pozidriv. It is a later development by the same company. The description of the Pozidriv head applies also to Supadriv. While each has its own driver, the same screwdriver heads may be used for both types without damage; for most purposes it is unnecessary to distinguish between the two drives. Pozidriv and Supadriv screws are slightly different in detail; the later Supadriv allows a small angular offset between the screw and the screwdriver, while Pozidriv has to be directly in line. In detail, the Supadriv screwhead is similar to Pozidriv but has only two identification ticks, and the secondary blades are larger. Drive blades are about equal thickness. The main practical difference is in driving screws into vertical surfaces: that close to a near vertical surface to drive the screws into the drivers, Supadriv has superior bite, making screwdriving more efficient, with less cam out. Phillips II Phillips II recesses are compatible with Phillips drivers, but have a vertical rib in between the cruciform recesses that interacts with horizontal ribs on a Phillips II driver to create a stick-fit, and to provide anti cam-out properties (the ribs are trademarked as "ACR" for Anti Cam-out Ribs. French recess
French recess driver bit
This section needs expansion. You can help by adding to it. (June 2010)
Also called BNAE NFL22-070 after its Bureau de normalisation de l'aéronautique et de l'espace standard number. A cross-head screw with a two-step driver design, with the blade diameter stepping up at a distance from the point.
JIS B 1012
JIS cruciform driver sizes
Driver size Machine Screw Size
#1 M2, M2.2, M 2.5
#2 M3, M3.5, M4, M4.5, M5
#3 M6, M8
The JIS B 1012 is commonly found in Japanese equipment. It looks like a Phillips screw, but is designed not to cam out and will therefore be damaged by a Phillips screwdriver if it is too tight. Heads are usually identifiable by a single dot or an "X" to one side of the cross slot. Specific "JIS" standardized cruciform-blade screwdrivers are available for this type of screw. Mortorq
The Mortorq drive, developed by the Phillips
Square recess dimensions
Orange #00 #1, #2 1⁄16 in + 0.05 in (1.3 mm)
Yellow #0 #3, #4 3⁄32 in − 0.0696–0.071 in (1.77–1.80 mm)
Green #1 #5, #6,[note 1] #7 7⁄64 in + 0.090–0.091 in (2.3–2.3 mm)
Red #2 # 8, #9, #10 1⁄8 in + 0.111–0.1126 in (2.82–2.86 mm)
Black #3 #12, 1/4 3⁄16 in + 0.1315–0.133 in (3.34–3.38 mm)
Brown #4 5/16, 3/8 3⁄16 in + 0.1895–0.191 in (4.81–4.85 mm)
Close-up of a Robertson screw
A Robertson, also known as a square or Scrulox screw drive is
Close-up of Robertson drivers
Illustration from Robertson patent application
Advertisement: “A Study in Evolution”
US patent 161390, Allan Cummings, 1875, wood screw drives
Multiple-square drives LOX-Recess The LOX-Recess screw drive was invented by Brad Wagner, and fasteners using it are distributed by licencees Hitachi, Dietrick Metal Framing, and Grabber. The design is four overlapping square recesses, with 12 contact points, and is designed to increase torque, decrease wear, and avoid cam-out. Double-square
The double-square drive is two Robertson squares superimposed at 45° rotation, forming an 8-pointed star. The design is similar to a square drive (Robertson), but can be engaged at more frequent angles by the driver bit.
The triple-square, also known as XZN, is a type of screw drive with 12
equally spaced protrusions, each ending in a 90° internal angle.
Common sizes are 6, 8, 10, and 12 mm. The name derives from
overlaying three equal squares to form such a pattern with 12
right-angled protrusions (a 12-pointed star). In other words, three
Robertson squares are superimposed at a successive 30° rotation. The
design is similar to that of the double-square—in both cases, the
idea being that it resembles a square (Robertson) but can be engaged
at more frequent angles by the driver bit. These screws can be driven
with standard Robertson bits.
The 12-pointed internal star shape superficially resembles the "double
hex" fastener head, but differs subtly in that the points are shaped
to an internal angle of 90º (derived from a square), rather than the
120º internal angle of a hexagon. In practice, drivers for the
fasteners may or may not interchange, but should be examined carefully
for proper fit before application of force. A hex key should not be
used where a key of square cross-section is the correct fit.
Triple-square drive fasteners have been used in high-torque
applications, such as cylinder head bolts and drive train components.
The fasteners involved have heads that are hardened and tempered to
withstand the driving torque without destroying the star points. They
are commonly found on German vehicles such as Audi, BMW, Opel,
6 mm and 8 mm triple square drivers
End view of 10 mm triple square screw
Internal hex drives Main article: Hex key Hex socket
The hex socket screw drive has a hexagonal recess and may be driven by a hex wrench, also known as an Allen wrench, Allen key, hex key, or inbus as well as by a hex screwdriver (also known as a hex driver) or bit. Tamper-resistant versions with a pin in the recess are available. Metric sizes of the hex socket are defined by ISO 4762 (socket head cap screws), ISO 4026 (socket set screws with flat point), ISO 4027 (socket set screws with cone point), ISO 4028 (socket set screws with dog point), and ISO 4029 (socket set screws with cup point). The German company Bauer & Schaurte patented the hex socket 1936 in Germany, and marketed products based on it. The term "inbus" is derived from Innensechskant Bauer u. Schaurte (German: "Inner 6-edge Bauer & Schaurte"), analogous to the US term "Allen key". In many countries it is commonly but incorrectly called "imbus".
Double hex is a screw drive with a socket shaped as two coaxial offset hex recesses; it can be driven by standard hex key tools. The shape resembles triple square and spline screw drives, but they are incompatible. The radial "height" of each arris is reduced, compared to a six-point, although their number is doubled. 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.
Hexalobular sockets Main article: Torx Torx
The hexalobular socket screw drive, often referred to by the original
proprietary brand name
Some screws have heads designed to accommodate more than one kind of
driver, sometimes referred to as combo-head or combi-head. The most
common of these is a combination of a slotted and Phillips head, often
used in attaching knobs to furniture drawer fronts. Because of its
prevalence, there are now drivers made specifically for this kind of
screw head. Other combinations are a Phillips and Robertson, a
Robertson and a slotted, a
The Phillips/square screw drive, also known as the Quadrex or
Pozisquare screw drive, is a combination of the Phillips and Robertson
screw drives. While a standard Phillips or Robertson tool can be used,
there is also a dedicated tool for it that increases the surface area
between the tool and the fastener so it can handle more torque.
The Recex drive system claims it offers the combined non-slip
convenience of a Robertson drive during production assembly and
Phillips for after market serviceability. The Phillips
A combined slotted and
Type A clutch head screw
Clutch Head Driver Sizes
There are two types of clutch screw drives: Type A and Type G. Type A, also known as a "standard clutch", resembles a bow tie, with a small circular "knot" at the center. These were common in GM automobiles, trucks and buses of the 1940s and 1950s. Type G resembles a butterfly, and lacks the center "knot". This type of screw head is commonly used in the manufacture of mobile homes and recreational vehicles. The clutch head was designed to be driven with a flat-blade screwdriver as well as a clutch driver.
A thumbscrew is a type of screw drive with either a tall head and
ridged or knurled sides, or a key-like flat sided vertical head. They
are intended to be tightened and loosened by hand, and not found in
structural applications. They are sometimes also cut for Phillips head
or slotted screwdrivers as well as having the knurl for finger grip.
External drives External drives are characterized by a female tool and a male fastener. An advantage of external drive fasteners is that they lack a recess in the head, which can collect water, dirt, or paint, which can interfere with later insertion of a driver tool. Also, some external drives can be engaged from the side, without requiring large inline clearance for tool access, which allows their use in tight spaces such as engines or complex pipework. Because the heads must stand out from the surface they attach to, they are rarely available in countersunk or flush designs. Square
A square screw drive uses four-sided fastener heads which can be turned with an adjustable wrench, open-end wrench, or 8- or 12-point sockets. Common in the 19th and early 20th centuries, when it was easier and cheaper to manufacture than most other drives, it is less common today (although still easy to find) because the external hex is now cost-competitive and allows better access for wrenching despite nearby obstructions.
A hex screw drive uses six-sided fastener heads, and the fastener is known as a hex head cap screw. It can be turned with an adjustable wrench, combination wrench and 6- or 12-point sockets. The hex drive is better than square drive for locations where surrounding obstacles limit wrenching access, because smaller wrench-swing arcs can still successfully rotate the fastener. Metric sizes of the hex are specified by ISO 4032 and ISO 4033, plus ISO 4035 for Jam Nuts, and ISO 4014 and ISO 4017 for hex cap screws, ISO 4018 for Hex head screws (grade c).
A pentagon screw drive uses five-sided fastener heads, and the fastener is known as a penta screw or penta bolt. It is designed to be intrinsically incompatible with many tools. Since five is an odd number, it cannot be turned by open-end or adjustable wrenches, which have parallel faces (and thus require a fastener with an even number of sides). Moreover, it cannot be turned by typical consumer- and professional-grade socket drivers, which possess either six or twelve points (neither of which are multiples of five). Penta nut security fasteners also are available, which can only be driven by specialized five-sided socket drivers. Due to the difficulty of turning these fasteners without specialized (and uncommon) five-point wrenches such as hydrant wrenches, they are commonly used for tamper resistance by public utilities on water meter covers, natural gas valves, electrical cabinets, and fire hydrants.
A 12-point screw drive uses two overlapped hexagon shapes, one rotated by 30º. Standard 12-point hex socket bits and wrenches fit these screws. 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. Compared to Allen hex sockets, the advantages of these bolts include higher torque capability and the lack of a recess to trap water. A disadvantage is the extra cost involved in forming the heads.
A set of "secure" or otherwise less common screwdriver bits, including
Most of the following screw drives are considered tamper-resistant because of their obscurity. Tamper-resistant drives are commonly used on equipment such as home electronics, to prevent easy access thereby reducing the incidence of damage or improper repair. Equally, this can prevent people with the relevant technical knowledge from possibly performing a repair without having to return the unit to the manufacturer. However, widespread recent availability of assorted drive bits (including security types) minimizes this advantage, at least for some fastener types. True tamper-resistant screw drives include the breakaway head and one-way screw drives. In addition to screw drives, various nut drives have been designed to make removal difficult without specialized tools. Proprietary examples include T-Groove, Slot-Lok, Pentagon, Tork-Nut, T-Slope and Spanner designs. Breakaway head The breakaway head (also called breakoff or shear fastener) is a high-security fastener whose head breaks off during installation, during or immediately after the driving process, to leave only a smooth surface. It typically consists of a countersunk flat-head bolt, with a thin shank and hex head protruding from the flat head. 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. Either method leaves only a smooth bolt head exposed. This type of bolt is commonly used with prison door locks, automobile ignition switches, and street signs, to prevent easy removal. An alternative design leaves a low-profile button head visible after installation. In addition to breakaway bolts, breakaway nuts of similar design are available. In non-security applications, a breakaway head fastener is sometimes used as a crude torque limiter, intended to break off at an approximate torque limit. For example, certain toilet seat fastener bolts use a breakaway plastic nut, with the driver part intended to shear at a torque high enough to prevent wobbling, while not shattering the porcelain toilet from excessive pressure. 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. This drive type has the disadvantage of not being as precisely controlled as can be obtained by proper use of a torque wrench; applications may still fail due to either too little torque being applied to correctly fasten the joint, or too much torque being required to shear the head, resulting in damage to the material being fastened. Bristol
Bristol Head Driver Sizes
0.069″ (4 flutes)
0.076″ (4 flutes)
The Bristol (or Bristol spline) screw drive is a fastener with four or
six splines, but is not necessarily tamper resistant. The grooves
in the wrench are cut by a square-cornered broach, giving a slight
undercut to the outer corners of the driver. The main advantage to
this drive system is that almost all of the turning force is applied
at right angles to the fastener spline face, which reduces the
possibility of stripping the fastener. For this reason Bristol screw
drives are often used in softer, non-ferrous metals. Compared to an
Allen drive, Bristol drives are less likely to strip for the same
amount of torque; however, the Bristol drive is not much more
strip-resistant than a
Line Head Driver Sizes
Internal External Tamper-Resistant
ALR3 ALH3 ALR3T
ALR4 ALH4 ALR4T
ALR5 ALH5 ALR5T
ALR6 ALH6 ALR6T
The line screw drive is a Japanese system with male, female and female tamper-resistant screw configurations. The fasteners are commonly called "line head screws". They are also known as "game bit screws", due to their use on some video game consoles. They are found on IBM computers, as well as Nintendo and Sega systems and their game cartridges. The female sizes are designated ALR2, ALR3, ALR4, ALR5, ALR6; the male sizes are designated with an "H" instead of an "R"; and the tamper-resistant female have a "T" at the end of the designation (e.g. ALR3T). In Japan, the male sizes are often designated as DTC-20, DTC-27, DTC-40 (discontinued) and DTC-45 corresponding to a respective screw head size of 3.2mm, 4.6mm, 6.4mm and 7.7mm; with the size of the screw measured across the widest portion of the mating part of the head. The most common sizes in use for consumer electronics are DCT-20 and DTC-27.
A one-way slotted screw
One-way screws are special screws that can be turned only in one direction. They are sometimes called one-way clutch screws, but should not be confused with true "clutch" screws. They can be installed with a standard flat-blade screwdriver, but cannot be easily removed using standard tools. One-way screws are commonly used in commercial restroom fixtures and on vehicle registration plates, to prevent vandals from tampering with them. One-way screws are practical only when the need for removal is unlikely. They are difficult to remove with conventional tools because the slot is designed to cause cam out when even minimal torque is applied in the direction to unscrew it. Instead, a special removal tool (a one-way screw extractor) must be used. Alternatively, a one-way screw can be removed by using a drill bit, by using a rotary tool and cutting disk to extend the slot, by using locking pliers, or by drilling two holes in the slot and removing the screw with a pin spanner (snake-eyes driver). It can also sometimes be removed by attaching a precision drill chuck tight to the screw head, in a manner similar to removing screws that have broken heads. Pentalobe
Main article: Pentalobe screw
The pentalobe screw drive (often mistaken for 5-point torx screw
drives) is a five-pointed tamper-resistant system being implemented by
Apple in its products. Apple's first use of the pentalobe drive
was in mid-2009 to secure the battery in the MacBook Pro. Smaller
versions are now used on the iPhone 4 and subsequent models, the
The polydrive screw drive, also known as RIBE, is spline-shaped with rounded ends in the fastener head. The tool has six flat teeth at equal spacing; the sizes are determined by the diameter of the star points. Its primary advantage over older screw drives is that it resists cam out. It is used primarily in the automotive industry in high-torque applications, such as brakes and driveshafts.
There are specialty fastener companies that make unusual, proprietary
head designs, such as Slot-Lok and Avsafe. These use special
circular or oval cam-shaped heads that require complementary socket
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. The
Ultra-Lok, and Ultra-Lok II are some of these designs that use custom
keyed drivers, which tend to be confined to industrial and
institutional uses that are unavailable to the average layperson.
Key-Rex screws are another design, and are used in such things as
ballot boxes and bank vaults.
One example familiar to laypersons is for the attachment of wheels and
spare tires of passenger vehicles to deter theft; one of the lug nuts
on each wheel may require a specialized socket provided with the set
of lug nuts. Similar security fasteners are also available for bicycle
wheels and seats.
A security hex screw drive features an extruded pin to make the fastener more tamper resistant by inserting a pin in the fastener screw drive, requiring a tool with a corresponding hole to drive the fastener. This can also prevent attempts at turning the screw with a small flat-bladed screwdriver.
The spanner or Snake-Eyes (trademarked) screw drive uses two
round holes opposite each other and is designed to prevent tampering.
Other informal names include pig nose, drilled head or twin hole.
This type is often seen in elevators and restrooms in the United
The 12-spline flange screw drive has twelve splines in the fastener and tool. It consists of 12 equally spaced protrusions, each with a 60° angle. It is achieved overlaying 4 equilateral triangles, each one rotated 30° over the previous one. The spline drive was part of the obsolete, U.S-designed Optimum Metric Fastener System and was defined by ASTM B188.8.131.52M, which was withdrawn in 2011, making the spline drive obsolescent. Spline drives were specified for 5, 6.3, 8, 10, 12, 14, 16, and 20 mm size screws. 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.
A set of torq-set bits
Torq-set is a cruciform screw drive used in torque-sensitive applications. The Torq-set head is similar in appearance to a Phillips drive in that it has a cross with 4 arms. In Torq-set however, the lines are offset from each other, so they do not align to form intersecting slots across the top of the head. Because of this, a regular Phillips or flat-blade screwdriver will not fit the head. It is used in military and aerospace applications. For example the E-3, P-3, F-16, Airbus, Embraer, and Bombardier Inc. Phillips Screw Company owns the name and produces the fasteners.
The applicable standards that govern the Torq-set geometry are National Aerospace Standard NASM 33781 and NASM 14191 for the ribbed version. The ribbed version is also known as ACR Torq-set.
The TA is a type of screw drive that uses a triangle-shaped recess in the screw head. Note that the sides of the triangle are straight, which differs from TP3 fasteners. Sizes include TA14, TA18, TA20, TA23 and TA27. These screws are often found in children's toys, particularly from fast food restaurants. They can also be found in devices such as vacuum cleaners, fan heaters, elevators, camping stoves, golf clubs, Breville kettles and Master Locks, among others, to help restrict access to the device internals. They can readily be driven with hex keys. TP3
TP3 (sometimes referred to as tri-lobe or tri-lobular) is a type of
screw drive that uses a Reuleaux triangle-shaped recess in the screw
head, so that it cannot be driven by a flat-blade screwdriver. It
is used on fast food promotional toys and video games, die-cast toys,
First row: Tri-Wing bits and screw head. Beneath: Tri-Point/Y-Type.
The tri-point or Y-type security screw head is similar to the Phillips
screw head, but it has three points rather than four. These
specialized screws are usually used on electronics equipment,
including the Nintendo Game Boy Advance,
Game Boy Advance
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.
The tri-wing, also known as triangular slotted, is a screw with three
slotted "wings" and a small triangular hole in the center. Unlike the
"tri-point" fastener, the slots are offset, and do not intersect the
center of the fastener. A version with left-hand threads is called an
Opsit screw, where unscrewing can be done by turning the screwdriver
clockwise, which is the opposite of tri-wing and regular
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.[citation
There are various other ways to categorize screw drives. One way is by shape of the fastener screw drive:
Hex Line (ALH) Square
Bristol Clutch Double hex Hex socket Hexalobular socket Line (ALR) Polydrive Robertson Spline TP3
^ Some specialty #6 Robertson screws require a Red #2 driver.
^ a b c d e f "screw drive systems". Sizes.com. 2010-12-30. Retrieved
^ Pavlis, Egon "arcticpenguin" [pseudonym]. "When a Phillips is not a
Phillips Plus So Much More!". Instructables: share what you make.
Instructables. Retrieved 2012-03-11.
^ a b c d Capotosto, Rosario (December 1996). "
Rybczynski, Witold (2000), One Good Turn: A Natural History of the
Wikimedia Commons has media related to Robertson screw.
Very comprehensive illustrated and annotated list of screw drive variants Phillips or Pozidriv? Spanner Jaw Sizes Security Fasteners at the University of Wyoming, featuring an extensive list of fastener insert designs When a Phillips is not a Phillips When a Phillips is Not a Phillips Plus So Much More! Quick Screws S