DIN 603 Carriage Bolts, Coach Bolts or Cup Square Bolts are listed below. Characterised by a flat mushroom or dome head, with a square section under the head to ensure the bolt does not rotate once fitted correctly. Available in A2 and A4 grade stainless steel and also Bright Zinc Plated steel grades 4.6 and 8.8. Used primarily in wood constructions but not to be confused with Coach Screws, Carriage bolts are secured by the use of a nut and do not cut thread when tightening into position.