Carriage bolts (round head with a 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.
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 imported stock carriage bolts have a thread length of 6″ and are fully threaded when the bolt length is 6″ or short
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Bolt Diameter
D
C
H
P
F
Body Diameter
Head Diameter…