AR Blue Clean 5 piece O-Ring kit for 100 Series model high-pressure hoses with the silver metal tip. Part # PW909110K.
Replace o-ring where metal tip of the HP hose where it connects to the spray gun.
Replace o-ring and install on the 1st indentation closest to the end of the metal tip.
Don’t use for the 2nd larger indentation on the metal tip (next to the HP hose side) as it does NOT have a o-ring.