While the majority of the wagons were built as HAAs, the final batch (built in 1982 as 368000-368459) were coded as HDA to indicate their ability to operate at up to 60 mph when empty instead of the standard 45 mph. This was achieved through modifications to the design of the brakes. Another variation, which did not initially result in a change of TOPS code, was the fitting of top canopies to increase the load volume. Many of the early wagons had these but then lost them and for some years canopied hoppers were only common in Scotland.