Intro to Millwright Practice Exam 2026 - Free Millwright Skills Practice Questions and Study Guide

The correct answer is a lag bolt. Lag bolts, also known as lag screws, are designed with a hex-shaped head, which allows for easy engagement with tools for installation. The coarse threads along their shaft enable them to grip securely into wood or other materials, making them ideal for heavy-duty applications such as securing beams or heavy pieces of hardware. The box or hex head is particularly useful because it can be turned with a wrench or socket, providing the leverage needed to drive the fastener into its material.

Other fasteners, such as machine screws, typically have finer threads and are designed to be used with a nut or in a tapped hole, while self-tapping screws have unique threading that allows them to create their own hole as they are driven in. Wood screws, while similar in application to lag bolts, generally feature a tapered head and finer threads that are designed specifically for fastening into wood without requiring a pre-drilled hole. In contrast, lag bolts provide a much stronger connection due to their larger size, hex head, and coarse threading.