Technical Specification ypically, machine bolt sizes range from 1/4" to 1 1/4" for square heads and 3/8" to 1 3/4" in diameter for hex heads, and lengths span from about 3/4" to 18" for square and 6 1/2" to 24" for hex heads. Measure length from under the head to the threaded end of the bolt. Both square and hex heads are available. Features - Enhanced durability. - Flawless finish - Easy installation