Discovery valves and caps do not fit Maximus models. For Maximus I suggest using the Marauder stem, ultra-light valve spring and upgrade valve screws I have listed. It shoots great with those upgrades at 2400 PSI with a Magnum Hammer Spring and Magnum Adjuster.
This Discovery valve has a bypass cap and ultra-light spring. It eliminates the pressure gauge on the tube. This makes assembly much easier and simplifies the tube assembly when mounting a tank or fill adapter with a gauge on it. The ultra-light spring produces a significant power increase. The valve is otherwise unmodified producing more power while maintaining excellent efficiency. It fits all the standard and custom Discovery tubes I have listed.