Claypit Clowns is a magazine story.
One day, the Fat Controller asks Bill and Ben to help Thomas and Percy at the Goods Yard. Bill and Ben sort out Thomas and Percy's trucks, but, as always, they decide to have some fun. So they switch Thomas and Percy's loads. At the bakery, Thomas is very embarrassed when the bakers unload the trucks and find that there is cement in the sacks. Meanwhile, at the building site, the builders discover that, instead of cement, they have been given trucks of flour.
The next day, the Fat Controller calls Bill and Ben's drivers over. The bakery and the building yard have some presents for them - bricks made out of flour and water and rock cakes made out of cement. The drivers are embarrassed and promise to be more careful in the future, while Bill and Ben just laugh.