Theory:

Thermal Expansion
The expansion of a substance on heating is called the thermal expansion of that substance.
Uses of thermal expansion

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 onto the rim of the wooden wheel.

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Wooden (Cart) wheel with an iron rod

Now the iron ring is heated to a higher temperature, it results in the expansion in the size of the ring, and the hot ring is then easily slipped onto the wooden wheel's rim. Coldwater is poured on the iron ring to contract in size and hold the wooden wheel tightly.

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The iron ring fitted on the wooden wheel

2. Riveting

Riveting is one of the most cost-effective and superior methods of fastening (join two parts). Rivets have a head on one side, a tail on the other used to join two steel plates together. Hot rivet is forced through the hole in the plates. One end of the rivet is beaten to make a new rivet head. When cooled, the rivet will contract and keep the two plates tightly together.
 
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Joining two parts using rivet
 
3. Gaps are left in between the rails while laying a railway track.
An increase in temperature during the summer days causes expansion in rails. So, in order to permit expansion at the joints of the rails, a slight gap is provided in between the rails while fixing a railway track.
 
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Gaps in the rails
 
If such a gap is not left at the rail's joints, the track will deform due to thermal expansion. It will cause derailment of trains.
Reference:
https://pxhere.com/en/photo/854017