New version with 4mm output shaft. Fits all 20 mm Brushless motors with 2mm shaft. Built-in cooling fins for cooler motors. 10mm x 10mm mounting box fits most planes designed with GWS gearboxes and any 10mm (3/8") square sticks. Comes with complete gear set assortment including 6.6:1, 5.3:1 & 4.4:1. All included pinions are for motors with 2mm shafts. Dual ball bearings and hardened shaft.