A word from Tridos Designs Our TDC replaces traditional hop-up arms with CNC machined aluminum nubs that provide perfectly vertical pressure to the bucking. Each TDC comes with 3x different nubs so you can choose whichever you like the best or use the red universal nub with any off-the-shelf nub like ML Omega / Panthera / soft nub / etc. *This is the PRO version Easy Installation We made sure that our TDC 2.0 can be installed with any level of skill. We made sure that our drill jigs are usable with handheld drills, the process is dead simple and there's no way you can mess it up. The drill bit also comes with a little shelf to make the pin removal easier on the Action Army chamber. Pro vs. Basic PRO version provides the absolute perfection in terms of feedback and looks. The external aluminum housing provides a satisfying click to the thumbscrew that allows to precisely adjust the TDC and protects the screw from accidental bumps. It also acts as an extra safety layer to make sure the screw doesn't turn by itself. BASIC version provides the same internals and performance of the TDC 2.0 PRO but at a more affordable price point, just without the external aluminum housing (clicking mechanism). Materials All of the parts in the kit, except for the drill jig, are CNC machined aluminum and Nylon (some pictures can be outdated). Everything is made to fit flawlessly together with no wobble whatsoever. They look and feel exceptional. Required for installation: drill or drill-press beer (optional) Compatibility TDC 2.0 is compatible with any bucking / r-hop. Compatible only with non-bridged barrels. An SSG10 w/ Action Army hop up unit. Includes Included in BASIC & PRO: 1x 9.0mm thumbscrew 2x o-rings 1x M3 grubscrew 1x nylon arm / insert 1x insert raiser 1x custom M3 aluminum nut 3x different aluminum nubs (black, gray and silver) 1x universal nub (red) 1x set of drill jig 3.5mm drill bit Included only in PRO: 1x external housing 1x plunger (pre-installed) 1x spring (pre-installed) 1x M3 set screw (pre-installed) 1x spare set of double sided tape