Durex (no sniggering at the back) was the cycle parts brand of Präzision-Werke Bielefeld, often shortened to PWB. Unsurprisingly, this was a precision engineering business based in Bielefeld in Germany. It is possible that PWB was founded in 1903.

PWB manufactured a range of products, particularly hubs with back-pedal brakes, and in the 1930s they produced rather simple, basic derailleurs under the Durex brand. After the Second World war they manufactured Simplex derailleurs under license - however these were not branded Durex but were branded Simplex. PWB added a subtle 'D' stamped onto them to indicate that they were made by Durex or in Deutschland or, perhaps, both.