A bench vice is probably the single most valuable tool you can permanently mount in place. If you can hold whatever you?re working on firmly and steadily in place, you?ll find the outcome vastly better ? in terms of results, ease of use, and safety. There are two primary aspects that determine a bench vice?s size ? width and opening depth. The vice is normally specified by width alone ? eg a ?100mm engineer?s vice?. The ?engineer? bit means that the vice is designed for metalworking rather than woodworking, while the ?100mm? refers to the width of its jaws.