This adapter connects normal North Americal male garden-hose style threads to a weird 5/8" UNF 18TPI thread socket. An 11/16" o-ring will fit snugly in the socket.
My boss' pressure washer, a Simoniz model, is plugged or seized in an area which can't be opened and cleaned. With this adapter, I hope to plug a garden hose into the outlet of the pressure washer, to force the clog back out of the partially disassembled valve. Wish me luck.
Table I found the right thread size in:
(Microphone stand listed as a source because it's another re-use of my openscad thread generator.)