Most
tamper-resistant screw configurations rely on the common unavailability of corresponding drivers to reduce the likelihood of widespread tampering. True tamper-rather than merely tamper-screw drives include the breakaway head and one-way screw drives. Both tamper-proof and tamper-resistant drives are commonly used in vandalism- and attack-prone areas, such as public restrooms, prisons, and banks; tamper-resistant in similar applications, and on equipment such as
home electronics, to prevent unauthorised access and repairs.
Drive bits for most standard security types have become available, making them secure only against casual adversaries not equipped with security bits. It is of course always possible to design new drives resistant to existing drivers available to unauthorised users, until they too are developed. 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 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.
Line Head and Line Recess Line Head and
Line Recess screw drives are Japanese systems with male, female and tamper-resistant configurations. The fasteners are commonly called
line head screws. They are also known as
Gamebit screws, due to their use on some video game consoles. They are found on
IBM computers such as the
PS/2, 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).
Oval Some consumer appliances, such as
espresso machines from
Jura Elektroapparate, use a proprietary screw head with an eccentric oval to discourage owners from servicing their machines.
Polydrive 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.
Proprietary head 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 drivers. 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. or
Snake-Eyes (trademarked) 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. Other informal names include
pig nose,
drilled head or
twin hole. 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. The driving tool is called a "spanner driver" or "spanner screwdriver" in the US, and a "pin spanner" in the UK. They are also often used for soft spikes on golf shoes. The US military's
M17 and M18 service pistols (variants of the
SIG Sauer P320) use spanner screws to dissuade disassembly of the handgun beyond normal field maintenance except by the authorized armorer; they have also been used previously for reinforcement screws on the
M14 rifle in order to secure the front locking tab on the magazine well, and are commonly found on the recoil lug of surplus rifles. Additionally many firearm trigger locks are simply spanner screws, with the appropriate driver serving as the key. The knife manufacturer Microtech uses a variation of this with 3 round holes arranged in a triangle shape. The camera company
Leica Camera has used versions of this on rewind knobs and other levers on their
rangefinder cameras.
12-spline flange 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 B18.2.7.1M, 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. Care should be taken not to confuse the name of this pattern with the casual phrase "spline head" which usually refers to the
XZN pattern.
Torx Plus Tamper-Resistant The tamper-resistant variant of Torx Plus, sometimes called
Torx Plus Security, has a center post. It is used for security as the drivers are uncommon.
Tri-angle The
TA is a type of screw drive that uses a triangle-shaped recess in the screw head. This drive can restrict access to the device internals but can readily be driven with hex keys. 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, electric kettles and Master Locks, among others. Sizes include TA14, TA18, TA20, TA23 and TA27. The bits are sized by the
altitude measurement of the equilateral triangle. Note that the sides of the triangle are straight, which differs from Tri-point-3 fasteners.
Tri-point and screw head. Beneath: Tri-Point/Y-Type. The
TP (or
Y-type) security screw drive is similar to the Phillips screw head, but with three points rather than four. These specialized screws are usually used on electronics equipment, including some
Nintendo handheld hardware, Sanyo and Kyocera cellular telephones, and Fuji digital cameras.
Apple uses Y-type screws to secure the battery on the 2010 and 2011
MacBook Pro, as well as an extremely small type in the
Apple Watch,
iPhone 7 and
iPhone X. This style of screw is often called a "tri-wing", although that name more properly belongs to a different design (see below).
Tri-point-3 rechargeable toothbrush, showing the TP3 headed screw used to hold the case together. When the rechargeable battery is no longer serviceable, the toothbrush case may be opened by removing this screw, allowing access to the battery and motor units for recycling. The wall adapter has a molded screwdriver on its case to facilitate this.
TP3 (sometimes referred to as
tri-lobe or
tri-lobular) uses a
Reuleaux triangle-shaped recess in the screw head, to make it semi-secure because it cannot be driven by a flat-blade screwdriver and is not readily driven, as Tri-angle is, by hex keys. It is used on
fast food promotional toys and video games, die-cast toys, and some
Roomba battery packs. There are four sizes:
A = 2 mm, 2.3 mm, 2.7 mm, and 3.2 mm.
Tri-groove 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.
Tri-wing 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 screws. 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.
McDonnell Douglas also used this as a primary fastener on its commercial aircraft. British Aerospace and Airbus are also users of this fastener. ==Other types==