Once had a set of tee shaped thingos for getting internal measurements, the cross section was spring loaded and once you put it inside object you twisted handle so it locked and then you could measure with mike.
Internal depth/bore/width gauge ;->
Not quite the same thing but internal callipers would do the same thing and the name might possibly have carried over.
For bigger bores you can get internal micrometers.
Micrometers incidentally are, according to Collins dictionary, also known as micrometer callipers. Not something I was aware of previously.
Erm dunno the one my father used to have was like two end to end but still spring loaded after the lock so you could remove it. Brian
Thanks to all, apparently they are called telescopic bore gauges (or gages if yank) I have discovered.
FWIW, Toolstation stock a cheapy set.
Internal bore gauges:
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