In 1920, the 16T diagram 97 mineral wagon was uprated to 18T capacity by fitting oil axleboxes and Spencer buffers. Builders included the NBR’s Cowlairs Works, R Y Pickering, Nelson, and Hamilton. Rather than tolerate private owner wagons on its rails, the NBR dedicated a large number of wagons to specific collieries’ traffic, by a process known as thirling. Such wagons carried both NBR and colliery insignia, and could be used on other traffic when coal shipments were light. These arrangements continued in LNER days.
Almost 3,000 of these wagons were built, including two batches after the grouping, which originally received LNER series numbers before being renumbered several years later into the ex-NB 7xxxxx series. Some wagons were built with standard NB buffers, and other wagons later received them at overhaul. In common with other oil axlebox wagons, the capacity was increased during the Second World War, from 18 to 20T. BR inherited 2,309 wagons in 1948. Withdrawal dates are not known, but some probably survived until the early 1960s. Whilst their main area of activity would have been the industrial areas of Scotland and the Border counties of Northern England, their use further south has been documented.
The photo shows a 16T wagon with grease axleboxes.