In 1983 the tanks from JOA class wagons 11312, 10202 and 740 were mounted on the QJG class flat wagon chassis from QJG12154/6/7 to create class JOB. A further conversion in 1984 involved JOA 10082 and QJG 12151. The JOB class wagons retained the QJG numbers.

The QJG's had originally of course been JG class water tankers.