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.
Now the iron ring is heated to a higher temperature, it results in the expansion in size, and the hot ring is then easily slipped over to the wooden wheel's rim. Coldwater is now poured on the iron ring so that it contracts in size and holds the wooden wheel tightly.