These applied synchronizers to match equipment speeds, making it possible for for smoother shifts and easier driving. The mid-20th century saw the introduction of automatic transmissions.  Primary Shaft is also referred to as output shafts. It revolves at a different speed in addition to offers required torque to the cars. https://israelvccbx.luwebs.com/34835448/automobile-gearbox-things-to-know-before-you-buy