The class Sk3 that was created in 1942 consisted of 88 locomotives which had been built by four different manufacturers, but were largely similar. All were 2-6-0 two-cylinder cross compound 2-6-0 locomotives for mixed traffic. Their service weight was between 33.5 and 35.3 tonnes and the cylinders had diameters of 400 and 580 mm, and a stroke of 600 mm. They were either wood-fired with seven cubic metres of wood in the tender or coal-fired with 5.5 square metres of coal.

The SLM in Switzerland built five in 1892 and eight in 1898 which were designated G3. The G5 consisted of five locomotives built by Dübs in Scotland in 1894. The German BMAG built a total of 26 G10 in 1901. Finally, the Finnish company of Tampella built 44 G11 between 1901 and 1905. They got the nickname “Mummo”, what means “Grandma”. The last ones had been equipped with a Dultz intercepting valve and all others were retrofitted in the twenties.

In 1942, the four types were consolidated into the class Sk3. After being used for goods and passenger service in the beginning, they were later used for shunting and construction trains after new locomotives had taken over their original tasks. Most were withdrawn in the fifties and the last one was gone in 1960. No. 400, built in 1903 in Finland by Tampere, is the only one that was preserved.