Lag Bolts/Lag Screws Known as lag bolts or lag screws or coach screws, these are among the toughest fasteners used in the industry. These extremely sturdy fasteners are usually used to connect heavy lumber or other heavy materials that bearing intensive loads. Their distinctive feature is their huge size with their starting size being approx. 20mm long and about 6mm thick. Lag screws have sharp lead thread points and are usually hex head.

Bolts can be described as long shafts with a distinct head on one side. These are generally partially threaded.

A fully threaded bolt is referred to as a screw.