We stock Galvanized, Stainless Steel and Zinc carriage bolts in diameters from 14" to 1-14" inches and lengths up to 18" inches. Carriage bolts have a rounded head with a small square section underneath. They are self-locking when placed through a square hole in a metal strap, or a round hole in most wood. This allows the fastener to be installed with only a spanner or wrench, working from one side.