As the I K, the Royal Saxon State Railways ran a type of very light and compact, six-coupled tank locomotive for 750 mm gauge. They were developed in order to obtain a cheap locomotive for the many narrow-gauge lines opened in Saxony from 1881.

In accordance with the intended use, the engines were simply constructed. In most engines, all three axles were fixed inside the frame, but the small wheel diameter of only 760 mm also allowed a short overall axle base, which is why sufficient running properties were achieved on the winding routes with tight radii. Only four of the 39 locomotives had a Klien-Lindner hollow axle installed at the front, but this was not used on the latest engines. Due to the short wheelbase, the boiler protruded beyond the outermost axle at the front and rear. The chimney had a clearly visible spark arrestor, since the area of operation of these narrow-gauge railways naturally often led through forests. The rope and the guide rollers of the hoist line brake, which was used to brake the train, were also visible.

Despite the very modest performance, 27 examples were taken over by the Reichsbahn after five had been handed over to Poland as reparations. They were given the numbers 99 7501 to 99 7527, but were retired before the late 1920s. Two of the Polish locomotives had returned to Germany during the Second World War, but were returned immediately after the war due to the availability of more powerful standard locomotives.

As a conversion from the I K, two Fairlie locomotives were created, which were created by coupling two locomotives each to the rear. This was done by removing the rear wall of the driver's cabs and thus connecting them to one driver's cab. These locomotives did not prove themselves, however, as the fireman had great problems loading the two boilers in the very narrow space. Two similar engines had already been manufactured by Hawthorn in England and these were also designated II K. These are also presented in a separate article.

Also worth mentioning is the replica of an I K as a museum locomotive, which was built in 2006, i.e. 125 years after the opening of the Saxon narrow-gauge network. This happened with the help of various sponsors and the support of companies, so that the engine could be completed in June 2009 in the Meiningen steam locomotive works and the total costs were significantly lower than originally estimated. Since then it has been in service with the Preßnitztalbahn.