Hillman Fasteners 240321 Carriage Bolt, 1/2-13 x 4.5", 25 PackCarriage bolts 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. 25 Pack 1 2 13 x 4. 5" Carriage bolt Steel round head Square neck Carriage bolts have a large smooth head Uses a 7 16 In wrench Zinc plated Coarse thread.