Round head bolts feature a button head and are largely used in wood connections. Round head bolts are same as the carriage bolts; however, they don’t have the square neck. As round head bolts are mostly used with wood, they do not exhibit high strength and are usually supplied in a standard ASTM A307 specification.
Standard Thread Length
Bolt lengths ≤ 6″: Thread length = (2 X diameter) + 1⁄4”
Bolt lengths > 6″: Thread length = (2 X diameter) + 1⁄2”