MODIFY Full Tune-up Kit for M4-A1 / RIS / SR16 (Speed ??16.32 / S100 +) Modular Gear Set + Cylinder + Piston head + Stainless Bushes + Cylinder head + Anti-reversal Latch + Tappet + Rotary spring guide + Ultra Piston + Nozzle + Spring + Synthetic Lubricant With PTFE.<br />