July 22, 1971 was a significant milestone in the history of the Bührer Tractor Factory. It was with great joy and pride that Rosa and Fritz Bührer, together with their sales manager Ernst Oberhänsli, handed over the 20,000th Bührer tractor to the family of Adolf Müller-Zellweger, resident in Wohlen AG, at a small ceremony in the spacious exhibition hall of the Bührer tractor factory. This was a Bührer tractor of the OP 17 model, equipped with a 55 hp Perkins engine. Up to this point, no other Swiss tractor manufacturer achieved such a large number of units as Bührer. Most Swiss tractor manufacturers were only able to build between 40 and 300 tractors before they had to stop tractor production. The most successful competitors were Meili with about 7000 tractors (1929-1969), Bucher-Guyer with about 5000 tractors (1954-1962) and Vevey with 3315 tractors (1936-1962). The second largest tractor manufacturer in Switzerland - Hürlimann - built its 20,000 tractor only a few years later.