It was to start with released in 1939 for cars. It includes the fluid coupling and a few planetary gears. They collectively make 3 forward and a single reverse speed. There is not any clutch for engagement and disengagement with the engine. Bevel gearboxes have spiral and straight enamel https://trentonypzba.techionblog.com/33821867/the-smart-trick-of-gearbox-that-no-one-is-discussing