Parts of a Fastener
Parts of a Fastener
- Screw Heads
The slotted screw drive simply has a single slot in the head of the fastener and is driven by a flat-bladed screwdriver. The slotted screw drive was the first to be developed and was for centuries the most common, simplest and cheapest drive to make. It works well when hand driven, but is not often used with power tools as the screw driver can easily slip out of the slot and damage the surrounding material.
The Phillips design was created by John Thompson. When he was unable to convince manufacturers to use his products he sold the design to Henry F. Phillips. Phillips is credited with forming Phillips Screw Company which promoted and improved the design. The original patent ran out in 1966 although the company continued to develop improved designs. Phillips heads were designed to cause the screw driver to cam-out. Cam-out is a process by which a screwdriver slips out of the head of a screw being driven in once the torque needed to drive the screw exceeds a certain amount to prevent overtightening. The term “Phillips” is used in everyday language to refer to any head style with a crossed recess but this usage is not always accurate.
The One Way Drive screw is a “tamper free” design. It is sometimes referred to as the one-way clutch. These screws are driven in with a standard flat-blade screwdriver but cannot be easily unscrewed because of the design. A special tool called a “one way tool extractor” can be used to unscrew it. Also various methods such as drilling, cutting, using locking pliers, and inserting a drill chuck into the head of the screw much in the fashion of removing screws with broken heads can be used.
The Hex Drive is a six point fastener head. It is often known as a hex head cap screw or a hex head machine screw. This head style can be driven with a wrench or with 6 or 12 point sockets.
The Hex Socket Drive has a rounded head with a hexagonal recess and is driven by a hex wrench often referred to as an Allen Wrench. There are tamper resistant versions with a pin in the recess.
Torx™ is the trademark for a type of screw head characterized by a 6-point-star-shape. It was developed in 1967. The official name given it by the International Organization for Standardization is “hexalobular internal driving feature”. The Torx™ is designed to allow for higher torque to be exerted on a screw when compared to a similarly sized hex socket head. Unlike Phillips drives, Torx™ heads were designed to prevent cam-out, allowing them to over torque the screw. Torx™ is commonly used in automobiles, computer systems, and consumer electronics. There is a tamper resistant Torx™ drive, which has a small pin inside the recess.