Upper Collar Type A ( Data Sheet DS 835 )

This nut has an internally and externally threaded piston. The external thread of the piston is fitted with a load retaining, locking collar. A gap is created between the nut body and the locking collar when pressure is applied. Again the gap is a combination of the compression of the bolted joint and gasket, if fitted, plus the elongation of the bolt.

In use the nut is pressurised until the hydraulic jack develops more than the desired pre-load. The locking collar is tightened. The pressure is released and the pre load is transferred onto the locking collar threads. Due to settling of the collar threads some of the pre load is lost. This is more critical in short bolt applications where the bolt elongation may be small. The pre-load loss on transfer to the collar becomes less significant on long grip length bolts.