Socket Head Cap Screws
Socket head cap screws are a special type of fastener. Socket head cap screws are typically used in machine parts, die fixturing, and clamping. Socket head cap screws are ideal for applications in which there is not enough space to maneuver wrenches or sockets.
There are a number of variations of socket head cap screws, including:
Socket head cap screws with nylon pellets that typically feature an internal hexagon drive (Allen head) that offers extra locking strength in the form of a small nylon pellet that’s applied to the threads to prevent loosening through vibration. It features a tall head and high strength.
Socket head cap screws with a nylon patch that performs the same function as the pellet. Like the previous socket head cap screw, this one is tall-headed, internally-driven, and high-strength.
Socket head cap screws with a full thread is another tall-headed, internally-driven high-strength fastener. The entire length of the shank is threaded, hence the name.
Socket head cap screws with a drilled head features a hole drilled in the head to accept a wire thread as a safety feature.
All of these variations on socket head cap screws feature tall heads and internal (Allen) hexagon drive as the most common drive. Socket head cap screws are also referred to as socket head bolts.
Socket head cap screws are not grade-designated like hex head cap screws. Standard inch series socket head cap screws are 20 percent stronger than a Grade 8 hex head cap screw and 50 percent stronger than a Grade 5 hex cap screw. The tensile strength is a minimum 180,000 psi for sizes 1⁄2′′ diameter and smaller and 170,000 psi for 5⁄8′′ diameter and above. Tensile strength may vary according to heat treatment and manufacturer.
Low head, flat head and button head cap screws — unlike socket head cap screws — are rated 10,000 psi lower due to the head configuration and are seen more in lighter duty applications.