If you pull out at the barrel more than 1.5mm, you really should use a gap-filling ring to maintain bore integrity. These are very easy to make these days. I have made most of mine from CDs or from the rings that come at the top of some CD spindles.
Tuning rings are put into the lower and larger end of the barrel, where you normally adjust for tuning. The point is that you don't want a gap in the bore like this:| | lower end of barrel
[ ] gap inside the bore
| | upper part of tenon on left hand keyed joint
The hole in a CD is just the right size (15mm) to fit virtually any clarinet. CDs can be cut with a sturdy pair of scissors.
- Start by marking and cutting a ring around the CD's hole that is just about the size of a quarter. Heavy-duty scissors work well for doing this cutting.
- Then, using a file, emery board, or sand paper, round-up and finish the ring so it will fit into the your barrel. It doesn't matter if it isn't perfectly round on the outside.
- Use sand paper or a file to make your ring the thickness you need.
Alan Segal sent this interesting comment:
Opperman was able to discern whether someone used a tuning ring or had merely pulled the barrel out without plugging the gap. I think Allard (your teacher) could do the same (these guys had great ears). Both recommended using the appropriate length of barrel if it was convenient to switch.