Some 20,133 of these 600cc shaft-drive, opposed twin R60 (1956-1960, 28 hp), R60/2 (1960-1969, 30 hp), and R60US (1968-1969, 30 hp) were built. These models, except for those with the "US" designation, were designed primarily as rugged motorcycles to pull sidecars (mounting points were built in) and had duplex tubular steel frames. In the United States, all these Earles-fork (see below) and US-fork (i.e., telescopic fork) models from 1955 to 1969 are often lumped together as "Slash-2" BMWs, even though that is technically incorrect. Not all over them, as seen above, have the "/2" designation.