8 mm reinforced gearbox v. 2 with ball bearings from SHS (ref. Super Shooter). Gearbox is made of CNC milled from high-strength aluminum 7075 (aviation alloy). Currently it is the most durable gearbox on market, which after proper installation and regular servicing it would be diificult for anyone to break!!! According to experience it has guaranteed durable resistance even on the strongest springs as the M190 from SHS. Supplied with ball bearings and set screws and washers beneath them.