This upgrade one-way fill nipple fits most PCP airguns including all Crosman / Benjamin models. It's made of stainless steel, extremely well machined and extremely reliable. The pin closes-off the opening to keep particles out between fills. After extensive problems with the various Crosman / Benjamin fill nipples over the years, and most others on the market, we've had excellent results with these. They're now the only ones we use for our custom airguns and fill adapters. The o-ring is 90D polyurethane which we have found to be extremely reliable for this application.