A Button Head Cap Screw (also known as a dome or Hex Socket Cap Screw) has a rounded head with a recessed hexagon drive that’s turned with an Allen wrench (hex key). This screw type is used in applications where bolts and nuts aren’t suitable, for example if the fastener needs to be tightened without removing the component being fixed.
The recessed design of the socket cap screw head makes it perfect for fitting into countersunk holes. This allows the screw to sit flush with the surrounding surface for a neat finish, and means there are no protrusions that could catch on clothing or skin. A hex socket screw has a wide load-bearing area and can be tightened to much higher torque specifications than normal machine screws.
These threaded fasteners are also known as hex bolts. Hex bolts are externally threaded, and have a six sided hexagon head for easy wrenching. They can be used with a washer and hex nut assembly or can simply be inserted into a tapped hole. They are popular for use with a wrench due to their high torque capacity.
Pan heads have a low domed profile and wider bearing surface than socket caps, they are designed for light fastening applications as their reduced head height doesn’t offer the same strength as traditional Socket Cap screws. They are however good for use in confined spaces as their low profile means they’re less likely to snag on moving machinery. They are also suitable for use with a captive washer or retaining washer. Button Head Cap Screw