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Conn Bore Sizes (Version 3)

This is a once again revised version of this bore size table, as of November 2006. I found the previous one to be mistaken, and I think I am closer to the truth.

I now suspect the bore sizes are fractions of 64ths of an inch. This causes the sizes to come out pretty close to what is actually measured on instruments, for the most part. The most important except is the #1½ bore size, which is generally accepted to be and usually measured as 0.458". By the logic of the table below it ought to be 0.453", but it isn't. Other deviations are the #½ (0.422" calculated, 0.425" usually measured), the #2 (0.4688" calculated, listed as 0.467") and the #3¾ bore (0.523" calculated, accepted as being 0.525", listed in Conn's 1966 catalog as 0.522").

In certain respects this table is also at odds with the measurements listed for some instruments in Dr. Margaret Downie Banks' book "Elkhart's Brass Roots". There are listed several instruments with a 0.433" bore and having a #1 bore (this would agree with my previous table and was also one of the foundations for that table). It is also interesting to note that in the "Elkhart's Brass Roots" book two instruments are listed that are said to have 1-1/2 stamped on the second valve. The bores sizes for these two instruments are listed as 0.445" and 0.447", which would correspond more closely to #1¼.

In an interesting discussion with Don "Relic Rescue" Rugg I learned of a better, more reliable, method of measuring bore sizes. In stead of measuring the inside bore size of the 2nd slide, first measure the outside diameter, then measure the thickness of the wall of the second slide at several points ("around the clock", so to speak). Take the average of these measurements and subtract twice the average wall thickness from the outside diameter. Keep in mind that when measuring instruments you are bound to come across some variation from one instrument to the next due to production tolerances or wear.

I would like to add that references to bore numbers such as "#1" or "#1½" can only be found on Conn instruments around the turn of the 19th and 20th centuries. Other than those instruments and the model number lists on R. Jones's site I have never seen references to these bore numbers in any Conn documentation I have found.

The column "Letters" refers to the bore size letters found on (mostly?) cornets in the 1910's.