Genuine STAXX Part #32302083 BF Top Nut

The top nut screws down into the hydraulic unit, housed in the top nut sit 2 seals a scraper seal and an O ring type seal

An O ring seal also sits into a groove just after the threads, this is to ensure the hydraulic unit is fully sealed and air tight

Fits Staxx models WH20L-51, WH-25ES-P, WH-25ES, BF30, BF25

Part 4 on the diagram