APS Metal Hop Up Unit For No.2 HYBRID V2 Gearbox Version 2 M4 M16 Series AEG Rifles AirsoftAPS One Piece Metal Hop Up Unit for No. 2 HYBRID V2 Gearbox Made out of metal. Designed for V2 Gearbox. Durable and accurate in feeding BB Improves Firmness of the chamber and stabilizes the muzzle velocity. Enhanced Hop Up Bucking for Accuracy. Fit tightly to the barrel base to keep the chamber being centered. Not like stock plastic chamber which would bend and de shape, this metal one give you rigidity. Highly recommend for upgraded Airsoft Electric