I have owned both a 2001 Sovereign and a 2007 Prestige. The tapered stem on the later German made horns was specifically made to be unscrewed since that is how the valve guides are changed. The guide is held in place with a positive ledge in the stem itself and cannot be removed unless one unscrews the stem. The English stem may be screwed in (I never had reason to take one out), but it is non-tapered and the guide is a friction fit into the recessed part next to the piston. One changes the guide by pulling it down over the upper part of the stem while the stem is still attached to the piston. The felts, dampers, and guides are the only interchangeable parts between English and German horns. The actual piston diameter and all of the threads are different.
Doug
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