3/8"-16 x 5-1/2" Zinc Plated Grade 2 / A307 Steel Coarse Thread Carriage Bolts 50PK, Midwest Fastener, Mfr#: 01107

A carriage 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.