1. Fitting the iron rim on the wooden wheel:
The iron ring is always made slightly lesser in diameter than that of the wooden wheel. Therefore, the iron ring cannot easily slip on it from the rim of the wooden wheel.
Wooden (Cart) wheel with an iron rod
When the iron ring is heated to a higher temperature, it results in the expansion in the size of the ring. Then, the hot ring is easily slipped over to the wooden wheel's rim. Coldwater is poured on the iron ring to contract in size and hold the wooden wheel tightly.
Iron ring fitted over to the wooden wheel