Coach screws are heavy duty screws designed for metal to timber connections, or to join heavy timbers. Coach screws are also known as lag bolts or lag screws, and they have a square or hexagonal head engineered to be used with a wrench, spanner, or pliers. Coach screws come in a wide range of sizes, from the very small ones packed with furniture designed to be assembled by the consumer to extremely big ones used in large scale construction projects. Hex Head