Forty-three of these 2,100-horsepower (1,570 kW) pacific locomotives were built by the Škoda Works, Plzeň in five series between 1926 and 1937, intended for the heaviest long-distance express trains.

The centre coupled axle, which is the driving one, has its flange reduced by 10 mm (0.39 in) to allow negotiate curves of 160 m (525 ft) radius.

The valve gear is of the Heusinger type, with internal link motion driven by flycrank on the left wheel of the rear coupled axle.

This arrangement proved itself very reliable in contrast to maintenance problems with the Gresley conjugated valve gear and was used for all subsequent Czechoslovak three-cylinder locomotives except of one series (Class 486.1).

The steam dome with throttle valve was on the first boiler ring and was cowled together with pneumatically operated sandbox.

After 1945 copper fireboxes were changed for steel ones, there were fitted Houlson grates and the arrangement of cylindrical boiler was also changed (134 large flue-tubes and 33 small flue-tubes with heating surface 230.1 m2 or 2,477 sq ft, large tube superheater with heating surface 60.1 m2 or 647 sq ft) and maximum speed was united at 110 km/h (68 mph).