Dunno what it's called – maybe double-ended caliper – but why not just make or find a flat piece of known thickness greater than the depth of border that fits inside the border, insert it, measure the total thickness, then subtract the thickness of the insert?

Edited By Mick B1 on 16/02/2023 16:02:04

Woodturners use this sort of thing.

Try Axminster Tools Under Woodturners Calipers

Michael G,

Do i correctly recall a Mobius Bottle?

Also I seem to remember something about a piece of amusing doggerel or poem about it?

Regards, Martin

.

Very nearly

**LINK**

https://en.wikipedia.org/wiki/Klein_bottle

MichaelG.

Yes, mobius was the first word that came to my mind when I looked at it.

Such double ended calipers are used by cylinder-head modifiers on car and motorbike engines for measuring how much thickness of metal is left between an enlarged port and thin air or the next port etc when grinding out the ports. So might be available from automotive tool suppliers.

Double glazing measuring tool…

https://www.upvchardwaredirect.com/double-glazing-measuring-tool-glass-gauge-15494-p.asp?gclid=EAIaIQobChMIgqXzzp-c_QIVyMLtCh2fhAATEAQYAiABEgIKnPD_BwE

Thanks. I think I had forgotten that the essential feature is that there are no conventional openings in the bottle.

Maybe a bit late to the thread but Ceramicists use similar items. Not with same size at both ends.

Link to one of the many suppliers here.

BPS

Edited By V8Eng on 17/02/2023 21:40:45

And if you do a google search for "Digital outside calipers" you will find this interesting mix of new and old tooling. Internal version is also available. Looks very handy for measuring oddly shaped things. And not very expensive at circa 30 Quid.

I have seen the figure 8 type referred to in an American cylinder head porting book as "indicating calipers" but a google search shows nothing under that except normal digital calipers and the above.

Edited By Hopper on 18/02/2023 03:57:45