The Köping–Uttersberg–Riddarhyttan Railway (Swedish: Köping-Uttersberg-Riddarhyttans Järnväg or KURJ) was a narrow gauge railway in central Sweden, 46 kilometers long. The railway went between the port city of Köping and small industry cities e.g. Uttersberg and Riddarhyttan in the northwestern direction. It existed 1864–1968.
This railway had a unique rail gauge of 1,093 mm (3 ft 7 in), which is said not to have existed anywhere else in the world. This happened by mistake. The railway was planned to have 1,067 mm (3 ft 6 in), a relatively common gauge in Sweden at this time, around 1860. Something went wrong when ordering locomotives and rail cars. Probably someone measured in the wrong way on the track, which was built from Köping and on. Possibly there was a mistake with the Swedish and English foot, which differ by about 2.7%.
When the trains arrived they did not match the railway, and it was considered to be cheaper to move one rail on the half-built railway, than to rebuild the vehicles.
In 1864 cargo traffic was started on a part of the railway. In 1866 the 35-kilometer-long Köping-Uttersberg railway was opened officially. In the year 1880 a new railway, the Uttersberg-Riddarhyttan railway was built by another company, with the same gauge. It was purchased by the Köping-Uttersberg company in 1911, and the combined railway was called Köping–Uttersberg–Riddarhyttan Railway. The passenger traffic was closed down in year 1952, and the last part of the freight traffic in 1968. All rails were afterwards removed.