Gearbox V2

Named for Tokyo Marui's original shell numbering, the V2 fits the M4/M16 stock tube and most carbine-length AEGs, which is why it has by far the largest aftermarket of pistons, gears, spring guides and shims of any shell type. Its main quirk versus other shells is the motor height and angle, set by the pistol grip geometry rather than the gearbox itself.

For a first-time tuner, V2 is the easiest shell to learn on: parts are cheap, tutorials assume it by default, and a bent stock tube is the only real obstacle to fitting stronger internals. Most technicians treat V2 fluency as the baseline before working on rarer shells.

Because so many manufacturers license or copy the same basic V2 layout, a part from one brand often fits another with only minor filing, which is the practical reason V2 internals dominate budget and mid-tier upgrade guides.