Plunger tube end cap also commonly knows as the "mickey mouse" is CNC out of billet NYLON.  A special depression is machined in to ensure that the main spring sits correctly in the plunger tube.  This feature is especially useful when modders use a mixture of springs in their plunger tubes.  Delrin, a self lubricating space age plastic is used to make the catch plate for smooth and trouble free operation.  Zero maintenance part that good for the stock plunger rod and especially good (almost crucial) for a metal plunger rod.  This is because metal on metal will cause friction and premature wear and tear.  So using delrin to engage and release a metal plunger rod will be effortless  while the material will be able to hold safely up to 20kg.  Anything beyond that is possible though we have not tested it yet.  This upgrade kit comes complete with an upgraded catch plate spring, useful for upgraded longshots