The locomotives were built in two main series, the first series from 1875 to 1884 and the second from 1898 to 1901.[1]
The later machines differed by the dimensions of the boiler, the shelter, suspension and appearance of the smoke box.[1] Some of the older series were eventually reboilered.
The Type 29 was very similar to the Type 28, from which it differed mainly in the diameter of the wheels (1.30 m instead of 1.45 m) and some details of the chassis.[1][1]
The machines used a Belpaire firebox and had an outside frame with the cylinders and the Stephenson valve gear located inside the frame.[2]