The UAC Match Grade Steel Hammer & Sear Set is constructed by precision CNC with carbon steel. The tight tolerance ensure the hammer & sear are in perfect shape. No burr is left behind, so no modify are needed. Also, titanium nitride (TiN) coating is used on the finishing to reduce the galling and friction. This is the most professional hammer & sear set ever made for airsoft TM G17 and perfect for competition. Tips: Just replace the TM stock hammer & sear with UAC Match Grade Hammer & Sear then use all TM stock rotor and springs. Please note: installing parts / assemble /fitting airsoft gun will need intermediate knowledge; for expert or airsoft gunsmith. Please refer to your airsoft gunsmith for proper installation / fitting. Fitting may be needed as the condition of each airsoft gun might be different.