Donn wrote:It could be simply radioactive decay of unstable isotopes.
If you have a reasonable set of drill twist bits, you can use them as approximate throat gauges. If not ... it's nice to have a reasonable set of twist bits. Sizes like 5/16, 19/64, 9/32. I think you're right, the throat is a place where a small difference is a big difference. Backbore shape too, but I have no idea how to compare that, between two different mouthpieces.
Yes, but when measuring, start with the shank end of the bit, not the tip end, so the sharpened flutes do not inadvertently scrape the interior plating.
The way I measure a throat is to take a drill bit that is slightly smaller, and then add one ring of masking tape at a time until the shank starts to drag through the throat, then take a micrometer to measure what I have, and adjust for any compression of the tape accordingly.
Most mere mortals play a mouthpiece that has a throat diameter that is a machinist's letter size drill bit, not a fractional size. An "O" drill bit is .316; a "P" drill bit is .323; a "Q" drill bit is .332. These three drill bit sizes are the throats or bore of the vast majority of tuba mouthpieces played in the USA, with a few smaller (especially for F tubas) and a few larger (according to the Bach mouthpiece manual, an 18 has an "S" throat).
As do many other people who do not play professionally and are starting to have to deal with limitations of breath support: I play a "P"; that rhymes with "T"; and that stands for...Tuba.
