What is this of clamp used for What type of screw thread is

What is this of clamp used for? What type of screw thread is used here?

1. G Cramps are an essential tool in the workshop and they come in a range of sizes and are generally used for clamping work securely to a surface/workbench top. They can also be used to hold parts together whilst glue is drying.

type of screw threads is square threads