Degrees of taper

[Mr.Gumby]

How about little disks,

Craig Fisher used to have that sort of sets available, for measuring (uilleann) pipes. But that was twenty years ago.

[Terry McGee]

Yes, the little discs idea has been around a long time. It has the slight downside that it always measures the minimum diameter, if the bore is out-of-round, but that's not a knock-out blow. You can modify them to explore minimum and maximum diameters if you want by ruling a line across one diameter, and then sanding the wood edges on the sides, being careful not to sand the disc at the end of the lines.

I use telescoping gauges such as those shown in trill's link. You need to extend the shaft to be able to explore deep into longer things.

[Terry McGee]

Note the difference in the end diameter between an old Clarke D and a C.Mathieu D (Ré), another antique.

Yeah, that looks a bit more robust.

The end of the Mathieu looks like it's been sharpened. For self protection in rough sessions back in their day? Or sees extra duty pipping olives?