Retro Arms, the Czech airsoft upgrade parts maker sent info about their new Retro Arms Version 2 Gearbox. These are fully milled gearboxes which we think are now using AW EN7075 T6 rather than 6061 T6... "The gearbox has long been tested on a spring M160 without any signs of wear and tear. Gearbox is fitted with 8 mm ball bearings, hardened steel connecting bolts and screws for mounting grips.