Carriage bolts feature a smooth, rounded head and a square shoulder beneath it that grips the material to prevent spinning while the nut is tightened.

Nominal Size: 3/16"
Thread: 24 TPI (Coarse)
Length: 4"
Thread Length: Full
Material: Steel
Finish: Zinc
Head Style: Carriage
Type: Carriage Bolt
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.