The ARES Ameoba / Ares M4 Series E.F.C.S. Metal Complete Gearbox Set is an upgraded version of the previous complete gearbox set that features a reinforced full teeth piston, gearbox shell, and an upgraded EFCS which is ARES' MOSFET system.
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Will fit most other brand's M4 / AR 15 series Airsoft Electric Guns. In some cases modifications might be required.