The South Australian Railways K class (narrow gauge) comprised a single locomotive. The design, by South Australian Railways Locomotive Engineer , was very similar to that of the broad-gauge K class, but it was smaller and lighter. It was allocated number 52 within the sequence allocated to the larger locomotives. The broad-gauge design was moderately "shrunk" to meet the smaller loading gauge of 3 ft 6 in (1067 mm) lines and the lower load-bearing capacity of track compared with the 5 ft 3 in (1600 mm) broad gauge. Some key specifications are compared in the table below.