These three diagrams together formed the largest group of BR Mk1 carriages. A side corridor gives access to eight compartments, divided into two groups by a central transverse vestibule with doors both sides. End doors were also provided. D146 had six seats per compartment with retractable armrests; D147 compartments had eight seats. D150 was effectively D146, but fitted with Metro-Schlieren bogies. All three diagrams have two toilets at one end, and a non-smoking compartment either side of the central vestibule.