What is a wagon solebar?

A wagon's solebar is the outer longitudinal beam of its underframe or chassis.

Solebars are an integral part of a wagon's frame to which several components and supporting cross members are attached. The solebar is also where you're most likely to find features such as the hooks for tarpaulin ropes and identification plaques such as maker and registration plates.

The underframes of wagons, including the solebars, were originally made from wood which lasted little more than ten years before requiring replacement, later frames were made from iron before steel became the production material of choice thanks to its greater durability and ability to resist rust for longer.