The Ares HPA Gearbox Set V2 for Marui and Ares M4 AEGs is a pre-installed, electronically controlled drop-in unit designed for High-Pressure-Air (HPA) setups. Featuring a pistol grip line configuration, it is compatible only with US-type air fittings – not suitable for EU-style connections. Designed for AR-15/M4 AEGs with V2 gearbox and single-sided selectors.