What material are soft jaw inserts commonly made of to protect metal surfaces in a vise?

Soft jaw inserts are commonly made of brass, which is the correct answer. Brass is chosen for its favorable properties in protecting metal surfaces because it has a relatively high malleability and ductility. This means it can absorb impact and stress without causing damage to the surfaces of the workpiece being held in the vise. Additionally, brass has good wear resistance, making it suitable for repeated use without degrading quickly.

Brass's composition also allows it to grip various materials effectively without marring them, which is particularly important in applications where the integrity of the workpiece surface must be maintained. This makes it an ideal choice for soft jaw inserts, ensuring that the metal surfaces are safeguarded during machining, assembly, or other operations.