At a minimum, a screw drive is a set of shaped cavities and protrusions on the screw head that allows torque to be applied to it.[1][2] Usually, it also involves a mating tool, such as a screwdriver, that is used to turn it. The following heads are categorized based on frequency,[citation needed] with some of the less-common drives being classified as "tamper-resistant."
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Slot screw drives have a single horizontal indentation (the slot) in the fastener head and is driven by a "common blade" or flat-bladed screwdriver. This form was the first type of screw drive to be developed, and for centuries, it was the simplest and cheapest to make. Additionally, it is unique because the slot head is straightforward to manufacture, and because it can be driven by a simple handtool. The slotted screw is commonly found in existing products and installations, along with use in simple carpentry work and in applications where minimal torque is needed. Slot screws are also used in the restoration of antique furniture, vehicles, and equipment.
ISO 2380-1[4] specifies the internationally standardized shape and dimensions of the tips of screwdrivers for slotted-head screws as well as the minimum test torque the blade-to-handle connection shall withstand. Screwdriver tips are generally designated by blade thickness width in mm, e.g. 1.2 6.5 which roughly matches a classic North American 1/4" screwdriver although the North American one is often a bit thinner (1.0 mm).
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.[6]
Coin-slot drives are so-called because of the curved bottom of the recess, which facilitates driving them with a suitable coin. 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.[citation needed]
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 advantage is that they provide some measure of redundancy: should one slot be deformed in service, the second may still be used.
The following are screw drives based on a cruciform shape; i.e., a cross shape. Other names for these types of drives are cross recessed, cross-head, cross tip, and cross-point. A double slotted screw drive is not considered cruciform because the shape is not recessed, and consists only of two superimposed simple milled slots. Some of these types are specified in ISO 4757, Cross recesses for screws.
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).[10] The numbers do not correspond to nominal screw size numbers. PZ1 is normally used on screw diameters from 2-3mm, PZ2 from 3.5-5mm and PZ3 from 5.5mm to 8mm. These sizes roughly correspond to the Phillips head numbers.
While a Phillips screwdriver has slightly tapered flanks, a pointed tip, and rounded corners, a Pozidriv screwdriver has parallel flanks, a blunt tip, and additional smaller ribs at 45 to the main slots. The manufacturing process for Pozidriv screwdriver bits requires a slightly more complex cutter than that for Phillips, however both can be manufactured in four cuts from a tapered blank.
Pozidriv and Phillips appear broadly interchangeable, but may cause damage if incorrectly used. Pozidriv screwdrivers will jam fit into Phillips screws, but when tightened they may slip or tear out the Phillips screw head. Conversely, while Phillips screwdrivers will loosely fit and turn Pozidriv screws, they will cam out if enough torque is applied, potentially damaging the screw head or screwdriver.[10][23]
The JIS B 1012 is commonly found in Japanese made equipment, such as cameras and motorbikes. Superficially it looks like a Phillips screw with narrower and more vertical slots, to give less tendency to cam out. The bottom of the recess is flat, and the point of the driver has to be blunt. A Phillips screwdriver has the same 26.5 degree cone angle but because of the tapered slots will not seat fully, and will damage the screw if forced.A correctly sized JIS driver will engage at full depth into a Phillips or Pozidriv head screw slightly loosely, but without damage. JIS heads are often identified by a single dot or an "X" to one side of the cross slot.[26]
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,[27] 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.[25][28][29]
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.[20] One advantage over the Phillips drive is that one driver or bit fits all screw sizes. It is often found in marine hardware and requires a Frearson screwdriver or bit to work properly. The tool recess is a perfect, sharp cross, allowing for higher applied torque, unlike the rounded, tapered Phillips head, which can cam out at high torque. It was developed by an English inventor named Frearson in the 19th century and produced from the late 1930s to the mid-1970s. The Reed & Prince Mfg. Company of Worcester, Massachusetts, was put into bankruptcy in 1987 and liquidated in 1990. Another entity called Reed & Prince Manufacturing Corporation, now of Leominster, Massachusetts, purchased some of the assets including the name at the liquidation sale.[30]
The Mortorq drive, developed by the Phillips Screw Company, is a format used in automotive[32] and aerospace applications. 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.[33] This low recess was able to create a shorter head height compared to other screws at the time of its development. This shorter head height was able to reduce the weight of this drive type. The Mortorq was originally designed for aerospace applications. This reduction of weight within the head height was able to create lighter assemblies for many aerospace projects. The materials used in aerospace applications are expensive, and the reduction of weight cuts down on the cost of production of these parts. This will allow thinner materials to be used for the screws. The shorter head height allows more "Clearance for internal parts and more design flexibility".[34] This allows the Mortorq drive to work in smaller and more complex builds.
The recess and driver were designed for "full radial contact along all four wings of the screw"[34] which helps to prevent stripping and cam-out. The straight walls in the design of the recess allow for almost all of the force of rotation to be used to drive the screw. When the bit is placed in the recess there is no wall contact until the driver is rotated, then there is full continuous contact to all four walls of the recess. The shallow recess allows for build-up and coating to occur without affecting the function of the driver. This shallow recess also grants off-angle drivability to allow work in hard-to-reach places. The design of the recess and shorter head height allows for more aesthetically pleasing work. This is in hopes that it will enhance the beauty and style of a product. Instead of covering up the screw head that it serves as an aesthetic part of the design. Ten different recess sizes are available for the Mortorq. The smallest of these, the PMT-000 can be used with screws that have a head diameter as small as 2.5mm. While the largest called PMT-7 can be used on screws with a head diameter of 35mm.[34]
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 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.[citation needed]
The hexalobular socket screw drive, often referred to by the original proprietary brand name Torx ( /ˈtɔːrks/) or by the alternative generic name star drive, uses a star-shaped recess in the fastener with six rounded points. It was designed to permit increased torque transfer from the driver to the bit compared to other drive systems. The drive was developed in 1967[41] by Camcar Textron.[42] Torx is very popular in the automotive and electronics industries because of resistance to cam out, and extended bit life, as well as reduced operator fatigue by minimizing the need to bear down on the drive tool to prevent cam out. A tamper-resistant Security Torx head has a small pin inside the recess. Owing to its six-fold symmetry, a Torx driver can also be used as an improvised substitute for a hex driver, although careful sizing is critical to prevent stripping the socket. 2ff7e9595c
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