Here you are Bazyle.

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That is how it is done/what it is for. Simple expansion experiment. for Physics or Science lessons.

edit: Fig 2 experiment

Edited By not done it yet on 29/09/2020 17:05:13

or these

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getting more expensive:-

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This is getting silly

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and just to be really silly, how about using some Cerobend – quite brittle but melts at just under 100 deg C, so would have to be kept away from the hot end of the bar – perhaps not !

Though I hate the mess cast iron makes I might have a go at a few to see if it can be done. One of the pictures in NDIY's link shows the pins are perhaps 2" long, length not critical.

I have a block of ex-night storage heater cast-iron full of awkward pockets. The plan is to hack a lump off with an angle grinder about 50mmx25x25" then slice it into 5x5x50mm square sections with a slitting saw, and finish off by turning them. Probably take 90 minutes each at £8.72 an hour to make 16 assuming no breakages! Bound to be a way of doing it faster, but what?

Dave