Special Cap Bolt Hexagon Socket Undercut Non Standard Steel

Special cap bolt is the bolt with a cap head and non-standard thread. Undercut often used at the end of the threaded portion of a shaft or screw to provide clearance for the cutting tool, and also referred to as thread relief in this context. Ever Hardware provides custom-made fasteners and customizable packaging.

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.

A rule of thumb is that the undercut should be at least 1.5 threads long and the diameter should be at least 0.015 in (0.38 mm) smaller than the minor diameter of the thread. Strictly speaking, the relief simply needs to be equal or slightly smaller than the minor diameter of the thread. Thread relief can also be internal on a bore, and then the relief needs to be larger than the major thread diameter. They are also often used on shafts that have diameter changes so that a mating part can seat against the shoulder. If an undercut is not provided there is always a small radius left behind even if a sharp corner is intended.