The Hillman Group 3491 1/4-20 By 1-Inch Stainless Steel Carriage Bolt, 10-Pack Carriage bolts are designed to fasten a wooden face to either wood or metal. Flat, smooth head eliminates the need for a washer Square underside of the head is self-locking to eliminate the need for a driving tool Features a 1/4-20 Coarse thread type