The Travelling Post Office, short TPO was first introduced in 1838. The TPO is closely linked with Rowland Hill's penny postage. They functioned as mobile sorting offices, allowing post officers to sort up to 2000 mails an hour while on the move.
The picture featured here shows a wooden and metal model of a mail bag exchange apparatus and forms part of a set.
Mail bag exchange apparatus's like this were used between 1852 - 1971 on Travelling Post Offices to pick up and put down mails without the need for trains to stop.
Mail bag exchange apparatus's operated by putting mail into leather pouches weighing between 20lb and 60lb that were attached to an arm which would suspend it 5ft above the ground and 3ft away from the carriage side. The carriage was equipped with a net, fitted to the side, with an opening into the carriage behind it to catch incoming pouches.