LEGO MOC 3-speed gearbox with comfortable manual step switch by Don_Santos | Rebrickable - Build with LEGO
LEGO MOC 2-Speed Gearbox by BD Technic | Rebrickable - Build with LEGO
Amazon.com: LEGO Technic COMPLETE GEARBOX ASSEMBLY 2 x 4 x 3 1/3 Trans-Clear Wormbox gear motor REDUCER block Mindstorms robotics ev3 NXT transparent robot building power functions part 6588 : Toys & Games
LEGO IDEAS - Lego 4x2 Truck With 16-Speed Transmission