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UNC Socket Head Cap Screws ASME B18.3-2012
Also known as an Allen screw or Allen bolt, or simply a cap screw, socket head cap screws are a more modern alternative standard machine fastener to the standard hexagon headed bolt or setscrew, as found on much modern machinery. A hex key (otherwise known as an Allen key) is required to fit these fasteners. Conforming to ASME/ANSI B18. 3, the contact surfaces of this screw or bolt are protected from external damage. Generally manufactured with a partial thread beyond a certain length and nominal diameter combination