A carriage bolt, coach bolt or round head square neck bolt is a form of bolt used to fasten metal to wood.
Class 4.6 steel carriage bolts can be used in automotive applications where they are commonly used to fasten light objects such as trim.
Carbon Steel, Alloy Steel
EN 10204.3.1 (2004)
Step bolts are literally used as steps on steel communication and electrical transmission towers. These bolts are generally provided with two A194 grade 2H heavy hex nuts. One nut is tightened against the thread run out. The unthreaded shank, or step length, typically ranges from 6″ to 10″. Step bolts are used for a variety of applications, including steel communication, electrical transmission towers, tower reinforcement. Moreover a host of other fastening jobs. The best step bolts feature low carbon steel bodies and high strength and are excellent for use with heavy hex nuts.
Step bolts are appropriately named because they are used as climbing steps on communication and utility poles and towers. They are also used to fasten wood to wood and wood to metal. As a member of the round head bolt family, they have a “large circular head with a low rounded top surface and flat bearing surface, and an integrally formed square neck under the head.” Similar to carriage bolts, step bolts may be the preferred choice for decking and soft wood because the lower profile head is less obtrusive, and the larger head diameter reduces the chance of pull-through. Since the head is designed not to turn, they are usually tightened by torquing a nut. Whenever the head is exposed, they can be used with an internally threaded (tapped) hole and tightened by turning the step bolt’s square neck.