Types of hexagonal socket screws

1. Hex socket head cap screws – standard

The head is 1.5 times the nominal thread diameter, making it a smaller diameter than most other machine screw heads.

When in use, the socket head cap screw is recessed within a counterbored hole 

so that the head is flush with the surface of the component being fastened.

This result is a clean appearance. There are no protrusions on the socket cap screw that could catch skin or clothes.

2. Button head socket cap screws

A hex socket button head cap screw is sometimes referred to as a dome or round screw. 

Button head socket screws characterised by their wide, load-bearing surface, which helps them resist loosening. 

The look is popular for aesthetic purposes, while the lack of sharp edges offers a measure of safety. 

The bulbous socket button head enables more torque than normal for greater clamping force. 

For best results, use a retaining washer to lock in place.

3. Countersunk socket screws  

Also called a countersunk hex head screw, or flat head socket screw.

The shoulder slopes at an 82-degree angle if imperial screws and around 90 degrees if metric screws. 

The head is designed to sit either flush with its surface or just below.