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 threads are standard 1/8 NPT tapered. The pin closes-off the opening to keep particles out between fills. After extensive problems with various fill nipples over the years we've had excellent results with this new design. They're the only ones we use for our custom airguns and fill adapters now.