This cap does not fit Maximus models.
For Discovery this cap is about 5/32" shorter to create a little more room in the tube for air. For 22XX it's intended for bulk-fill, HPA and PCP conversions. This and the Discovery valve stem I have listed are all you need to convert your gun to work with the MAGNUM TANK ADAPTER or a DISCOVERY FILL ADAPTER for bulk-fill. It's made of 6061-T6 aluminum for excellent strength and corrosion resistance.