Intro to Millwright Practice Exam

Which type of bolt has a rounded head and a box-shaped portion to prevent it from turning while the nut is tightened?

1. Hex Bolt

2. Carriage Bolt

3. Lag Bolt

4. Shoulder Bolt

The correct answer is: Carriage Bolt

The correct choice is the carriage bolt, which is characterized by its rounded head and a square section directly below the head. This unique design serves a vital purpose: the square section fits tightly into the material, preventing the bolt from turning when the nut is tightened. This feature makes carriage bolts especially useful in applications where a flush finish is desired, such as in wooden constructions or when fastening metal to wood. In contrast, a hex bolt typically has a hexagonal head that is designed to be turned with a wrench, without any special feature to prevent rotation in its hole, relying instead on friction or the use of washers. A lag bolt is a heavy-duty screw designed primarily for fastening wood and does not have the same head and square neck configuration found in carriage bolts. Lastly, a shoulder bolt (or stripper bolt) has a head and a shoulder (or neck) that is a specific length, allowing it to serve as a pivot point in machinery applications, but it does not possess the same rounded head and square neck as a carriage bolt. Understanding these characteristics ensures that appropriate fasteners can be selected based on the specific requirements of a project, enhancing both functionality and safety.