Carriage bolts (round head with square neck) are commonly used in wood connections. The square neck under the round head will seat into the hole in the wood to prevent the head from turning. Because they are used with wood, carriage bolts are rarely high strength and virtually always supplied in a standard ASTM A307 specification.
Portland Bolt manufactures carriage bolts from 1/2" diameter through 1-1/4" diameter in most ASTM, AASHTO, and SAE specifications. Special tooling can be created to produce nonstandard head dimensions, carriage bolts larger than 1" in diameter, or bolt heads with your company's name and/or logo.
Standard Thread Length
Bolt lengths ≤ 6": Thread length = (2 X diameter) + 1/4"
Bolt lengths > 6": Thread length = (2 X diameter) + 1/2"
Note: Most stock carriage bolts have extended thread length.
Diameters: 3/8" - 3/4"
Lengths: 18" maximum
Finish: Black and hot-dip galvanized
*Dimensions per ASME B18.5 1990 (R 1998) cover diameters up to 1". Bolts over 1" use custom head dimensions.