Heating the bar and then comparing it to the gauge provides an excellent visual demonstration of thermal expansion.
For illustrating expansion by heating and contraction by cooling.
Comprising a bar of iron mounted on a support rod with wooden handle, and a brass gauge with a cut-out which barely admits the bar lengthways while cold, and a hole which passes the bar endways only while cold. 

Physics School Lab Equipment Suppliers in India 

Ltekonline are the manufacturers of Bar and Gauge Apparatus Heat Lab used to demonstrate engineering principles in Engineering Colleges, Engineering Schools and Physics Lab Experiments for Engineering Teaching Lab in Universities