Major Japanese brake manufacturer. They used to have a working relationship with Sun Tour, and made the brakes that say «Sun Tour.» They were the leading Japanese brake supplier before Shimano acquired a near monopoly on the Japanese parts business. They have a well-deserved reputation for quality.
Dia Compe first made a major impression on the bicycle industry in the late '60's, when they invented extension levers for drop-bar brakes. At that time, Weinmann was the leading brake manufacturer. Dia Compe's extension levers were so popular that Weinmann entered into a licensing agreement with Dia Compe, allowing Dia Compe to copy Weinmann's brakes in return for letting Weinmann copy Dia Compe's extensions.
More recently, Dia Compe has revolutionized the design of headsets, with their «AheadSet» threadless headsets.