8mm ball bearings is to reduce the friction put on the gears fulcrum while spinning.
Designed to prevent damage to the gears and to prevent gearbox failure due to high stress .
Fit for M4 AEG.
This gearbox has an unique shell, spring guide, selector plate, cut-off lever and trigger, all other parts are compatible with regular AEG Ver.2 6mm M4 gearboxes.
Easy power upgrade system.
Full metal reinforced chassis / gearbox with metal gear set.

Including:
Aluminum Spring Guide With Bearing.
Aluminum Double O-Ring Piston Head With Bearing.
Double O-Ring Metal Cylinder.
M120 400 fps Spring
Aluminum Nozzle With O-Ring
8mm Bearing.
steel Metal Shell.

Weight(Gram):629 (With Box)