The wagon on which the model was based would have been built late in 1971 and marked the beginning of the air-braked fleet of long wheelbase (20ft 9in chassis) wagons that replaced the old 10ft wheelbase open wagons that dated back to the early days of the 20th Century. It was one of a batch of a hundred 45 ton open wagons built at Ashford. Under TOPS, the OAA code was adopted. They had 6-plank sides each dropping down in three sections. By 1991, almost all the wagons from this batch had been transferred to civil engineers use and carried the 'Dutch' grey and yellow livery seen on this model. They were also re-coded ZDA 'Squid', as seen here.