Re: What is this?
Reply #3 –
That plunger fits inside one of the HWH solenoid valves. It couldn't just accidentally fall out on the ground - the valve must be completely disassembled for it to be removed. See photo below for disassembled valve. The solenoid coil fits onto the chrome shaft. The chrome shaft must be removed from the brass valve body to reveal the plunger and spring.
See Reply #53 for the full disassembly sequence:
Brand New Replica HWH Plungers