8 mm reinforced gearbox v. 3 with ball bearings from SHS (ref. Super Shooter). Gearbox is made of CNC milled high-strength aluminum 7075 (aviation alloy). Currently it is the most durable gearbox on the market, which after proper installation and regular servicing would be very hard for anyone to damage!!! According to experience is guaranted durable resistance even on the strongest springs as the M190 from SHS. Supplied with ball bearings and set screws and washers beneath them.