In 1930 a new design of all steel bogie open wagon appeared (class RB). Construction continued until 1937 by which time a total of 177 had been built, however, during this period, forty of the first batch of these wagons were fitted with wooden side extensions and a ridge pole and reclassified RBW for bulk wheat traffic. These conversions occurred as follows:

1931	11185, 11192, 11208, 11213, 11216, 11217, 11218, 11219, 11228, 11229, 11243, 11263, 11269, 11275, 11276, 11277, 11291, 11296, 11299
1932	11186 11189, 11190, 11193, 11195, 11198, 11211, 11212, 11221, 11224, 11226, 11227, 11231, 11250, 11255, 11257, 11260, 11262, 11270, 11282

No more RB class wagons of any type were converted to this standard but the converted wagons lasted well. They were written off over the period from 1965 to 1990 as follows:

1965	11192
1970	11257
1972	11221
1976	11198
1979	11255, 11282
1984	11250
1985	11219, 11229, 11263, 11275, 11277
1986	11193, 11212, 11213, 11217, 11226, 11227, 11228, 11231, 11260, 11262, 11296
1987	11185, 11189, 11190, 11195, 11218, 11243, 11299, 11300
1988	11211, 11216, 11224, 11269, 11291
1989	11186, 11208
1990	11276