3/8-16 Carriage Bolt Hot Dipped Galvanized 307A Grade A Steel Coarse Thread. A carriage bolt, also known as a coach bolt, has a domed or countersunk head, and the shank is topped by a short square section under the head. The square section grips into the part being fixed (typically wood), preventing the bolt from turning when the nut is tightened.
All Carriage Bolts under 6 inches are fully threaded. Sizes over 6 inches in length have a shoulder.