Alexander screwbell rings are probably the most common bell rings used by cottage Horn makers and modifiers. They are very well made, reasonably affordable, and they are thought of as "standard" among the Horn playing community. One of the most frequently asked questions I receive about screwbell conversions is whether the rings I use are Alexander compatible (I use Alexander rings, so that goes without saying). The reasoning behind this question is that some people who have their bell cut entertain the thought of eventually trying different flares to change the sound of their instrument. There is, however, an issue. Alexander makes three different types of rings to correspond with the different throat tapers of their instruments. All of the rings have the same tread size, outside dimensions, and large diameter of the taper, but the angle on the inside is different. The diagram below is a cross section of one side of the ring.
Since the different rings have the same thread size and outside dimensions, they will thread together perfectly and look fine from the outside, but there will be a step on the inside due to the different angles as shown in the diagram below, which shows the female half (with the inside threads) of a small ring screwed together with the male half (with the outside threads) of a large ring.
You can see that, due to the different angles of the rings, there is a step at the joint between the two rings (The diagram is not an exaggeration as seen below). Likewise, the step would be reversed if the female half was from the larger ring and the male half was from the smaller ring as can be seen in this picture.
Obviously, if trying different flares for your Horn, it would be best to try flares using the same size ring (any difference will be obvious). If you put a flare from an Alexander 103 on your 8D, you're going to have a sizable step and the height of the flare might also be a bit different, since the rings will fit different bells at different heights. The inside edge of the bell can be pretty sharp even after it has been deburred. While it probably will not actually cut you, it will be quite uncomfortable and distracting since most players' knuckles will rest right on the joint This is probably not ideal for performing.
This begs the question, why doesn't Alexander make the diameter of the rings at the joint the same size regardless of the taper? If they did this, they would have to make the rings thicker in order to have the same thread size on the different rings. There would also be a greater disparity between the heights of the flares on bells with slower or faster tapers. For example, if the diameter of the ring at the joint was 75mm (nearly 3 inches), that point on a bell from an 8D would be quite a bit higher than that point on an Alex 103, making the latter flare useless on the 8D and negating the point of standardizing the ring. If you have any questions or comments regarding this, please feel free to contact me.
See the Screwbell Conversion page for more details.
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