Manufactured by Bruno Viertmann at Bielefeld, Beckhausstraße 1, between 1935 and 1941. 
The firm built lightweight motorcycles with Sachs 100cc engines and 120cc JLO-powered utility tricycles (Dreiräder). These were "muzzle-loaders" (front-loaders) with two steered wheels at the front and a single driven wheel at rear.
Viertmann's business exploits are well documented in the book Motorräder aus Bielefeld by Johann Kleine Vennekate.
Notes. 1. Production dates are a little hazy, GTU giving 1935-1939 and AOM 1938-1941/42.
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