The Railway Clearing House, originally set up by the railway companies to handle charges for vehicles used on another company’s line, introduced standard minimum specifications for private owner wagons. The RCH 12 ton design was the most numerous design of coal wagon built in the UK after 1923. A rugged and simple design employing standard RCH fittings throughout and originally they had to be built with seven side planks. Various configurations of side doors, end door and bottom doors were permitted, but the weight of the unladen wagon was not to be above 7 tons 5 cwt. Oil lubrication and brakes on both sides were mandatory. The main line railway companies adopted RCH fittings for many of their own designs, and the LMS and LNER adopted the RCH 1923 mineral wagon as their standard.