The Fz was a 2-6-0 locomotive for use on Riggenbach rack lines. They had two cylinders for adhesion service and two for rack sections. When all cylinders were used together, they could either be used in compound mode or all with high pressure steam. The first four locomotives were built for the line between Honau and Lichtenstein and the next five for the Murgtalbahn between Freudenstadt and Klosterreichenbach. The second batch had two domes which were interconnected with a tube.

They had lots of pulling power on the rack lines, but the boiler was not powerful enough to sustain its pressure on long climbs. So they sometimes had to stop to build up steam again. The Reichsbahn took over seven and numbered them 97 301 to 97 307. Their withdrawals came already in 1930, most likely due to the complicated valve gear.