BR had been rebodying 21ton hopper wagons for some years before it decided that new rebuilds would be renumbered and uprated to 25t. The vacuum brake HTV (just over 900) were B340xxx and the unfitted wagons HTO (about 1300) were B345xxx and 346xxx. Most had welded bodies but some had huck bolt construction with U channel stanchions. See the interesting comments from Andy Latham about the respringing and raising of the capacity to 25ton of the HTV and a few HTO which I have associated with B340516. Scale drawings in: Monk-Steel, David (2022) An illustrated history of British Railways Hopper Wagons. HMRS publishing, Butterley Station, Derbys. 248 + iv pages ISBN 978 0 902835 42 9
