Fitment: Fit for 1-1/2″ (or 38mm) cap nuts. This cap nut wrench is designed for old nut and thimble style semi truck lugs. Function: Designed to hold outer cap nut on dual wheels while the inner nut is turned. Used to break apart the cap studs and the nuts without damaging the wheels. Installation: Simply place the wrench with the lip against the rim and the wrench fit securely without rotating or slipping. Then use square drive to split cap studs and the nuts. Material: .