A set of "secure" or otherwise less common screwdriver bits, including secure Torx and secure hex or "allen" variants.

The chief disadvantage of Pozidriv screws is that they are visually quite similar to Phillips; thus many people are unaware of the difference and/or do not own the correct drivers for them, and often use an incorrect screwdriver. This results in difficulty with removing the screw and damage to the recess and/or driver, often rendering any subsequent use of a correct screwdriver unsatisfactory. Phillips screwdrivers will loosely fit in and turn Pozidriv screws, but will cam out if enough torque is applied, potentially damaging the screw head and or driver. Because the drive wings on a Pozidriv screwdriver are square edged, their fit in a Phillips screw head is even worse, so they are more likely to slip or tear out the screw head.

Most of the following screw drives are considered tamper-resistant because of their obscurity. The exceptions to this are the double hex and triple square screw drives that can be removed with standard hex or square screw bits. The first class of tamper-resistant drives is commonly used on equipment such as home electronics, used 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 security types. True tamper-resistant screw drives include the breakaway head and one-way screw drives.

The breakaway head (also called breakoff or shear fasteners)may be 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 in 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.

The Bristol screw drive is a spline with four or six splines, which are 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 Torx drive. It was created by the Bristol Wrench Company.

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. Variants with a pin in the center are often found in game systems.If you want to know more,please click www.din571.com