Numbered Drills and Horn Mouthpiece Bores


One question that came in today is one asked fairly often, about the numbers on horn mouthpieces. As in, what is 12, 8, etc.

Basically there is a set of machinists drills that are numbered and the numbers are similar to those used in wire gauge as well. The ever-useful-for-general-information Wikipedia reports,

Number and letter gauge drill bits are still in common use in the U.S.. In the past, they were popular elsewhere, but now have been largely discarded in favour of metric sizes….

Number drill bit gauge sizes are analogous to, but different from, American wire gauge.

There is a chart of the sizes in the Wikipedia article but in short all you really need to know as a horn player is that a #1 drill is the largest in the set. The photo shows my set I keep in my office, which runs from #1 to #20. Actually these drills are used, in smaller sizes, quite often in hobby applications. I have drills as small as #80 in my model railroad tools, that size being roughly the size of a small needle.

Some mouthpiece makers have for many years used these drills as the system used to measure the bore of horn (and trumpet) mouthpieces. So a C-8 should have a bore that just lets a #8 drill pass through but not #7, which is slightly bigger. Etc. The letter is an arbitrary designation for the shape of the cup, in this example the C being for a Chambers cup (for James Chambers, long time Principal Horn of the New York Philharmonic).

In terms of horn mouthpiece bores, the vast majority of players today use bore sizes ranging from #8 to #17. The set I keep in my studio is very handy to sort out what things really are, especially when comparing brands and models, it is easy to fool the eye.

University of Horn Matters