Wiring harness for NSU OSL 251 WH with cotton + wiring diagram : Amazon.co.uk: Automotive
Reifensatz für NSU OSL 251 - Heidenau : Amazon.de: Auto & Motorrad
Incredible Restoration for 1937 NSU OSL 251 Bike - autoevolution
An Illustrated History of Military Motorcycles: 100 Years of Wartime Motorcycles, from the First Machines of World War I to the Diesel-Powered Types and Quad Bikes of Today, with 230 Photographs: Amazon.co.uk:
NSU 251 OSL
Incredible Restoration for 1937 NSU OSL 251 Bike - autoevolution
1938 NSU 251 OSL specifications and pictures
NSU Motorrad, 251 OSL, Ersatzteilelistc (Spare Parts List in German): Motorrad: Amazon.com: Books