Gearbox

Three gears reduce the motor's high speed into the torque needed to pull the piston back against its spring, then release it to strike forward. Everything that defines an AEG's behaviour — rate of fire, trigger response, how hard it hits — traces back to what's inside this one shell.

Gearboxes are standardised into numbered shell types (V2, V3, and others) so aftermarket parts fit predictably across brands using the same shell. Opening one to shim gears, swap a spring, or fit a MOSFET is the single most common upgrade path in the hobby, and it's why AEGs stay serviceable for years past their factory internals.

A full teardown and rebuild is a genuine skill that takes several attempts to get comfortable with, so most first-time technicians practice on a cheap donor gearbox before opening the one in their main rifle.