This upgrade adapter is made of stainless steel. It's the standard one for Discovery models. It fits all 7/8" OD threaded Crosman tubes including Maximus, 2240, 2250, 2260, 2300 and 2400 models. I round-over the sharp edges on the hex lug so the cap snaps on and off smoother without damaging the internal o-ring that holds it on. The rounded edges can be seen pretty well in the third photo. I install the fill nipple with military-grade sealing tape. Cap included.