Found a deep well 36mm socket for an impact wrench so it's hardened steel, taking a while to get it down to fit on the pressure switch. Jim mentioned that it might take some effort to unscrew it as they seemed to have over tightened them at the plant. As I'm looking it I can see how it, the motor and accumulator are bolted to the master by just one bolt and worried about breaking them off! Will give it a try with some WD40 but obviously, not gonna reef on it.