Suitable for most jobs on metallic tubes.Self-locking function in both directions.Strong chain made of tempered special steel.Jaws and body in forged hardened steel.Double sided tooth system for ratchet-like use.Maximal tube capacity up from 38 mm (1-1/2") to 305 mm (12").Standards: US Norm GGG-W-651, Type I Class B, UNE 16555