Stainless Steel Carriage Bolt, 1/4 X 2-1/2 Inches, 25-Pack, Hillman 832522. Product Description Carriage Bolts are designed to fasten a wooden face to either a wood or metal frame. Its flat head is designed to eliminate the need for a washer and provide a semi-flush finish to applications. The square underside of the head is self locking to eliminate spinning and the need for a driving tool. Stainless Steel finish provides superior rust prevention, terrific for all outdoor applications. From the Manufacturer Carriage Bolts have a smooth, rounded head that has a small square section underneath. They are used in wood connections utilizing the square neck under the round head which will sit into the hole to prevent the head from turning. These carriage bolts come plated in zinc for moderate corrosion resistance. Carriage Bolts are designed to fasten a wooden face to either wood or metal Flat head provides a semi-flush finish to applications The heads is designed to eliminate the need for a washer Square underside of the head is self locking to eliminate the need for a driving tool Stainless Steel provided superior rust prevention and bright finish