The Bayliss-Wiley Unit Bottom Bracket was introduced in the mid-1940s. It was fitted to various English lightweights through the 1950s and was used by Royal Enfield on its 'Revelation' small wheeler in the mid-1960s. However, the unit bottom bracket was never popular and it had a reputation for being troublesome. A lack of positive location allowed it to rotate within the frame, loosening the bearing cups. Contemporary users overcome the problem by fixing the unit in the frame using adhesive or a screw.