All these carriages worked in sets with a corridor composite or corridor brake composite. The two batches had significantly different underframe arrangements; the kit is supplied as the 3 car set version. They were in service all over the Southern Region.
Please note that this kit represents the shallow vented (10¼”) version of D2123. A similar deep vented (15″) coach, to the same diagram number, is represented by our product S4K. Carriages 4349-4370 were also to D2123, but had extended side panels for use in Bournemouth 6 coach sets.