Don't know how that happened! I was going to say

Thanks Helen. Even the crown seals in home brewers' supply shops have plastic inserts these days. Fortunately I don't play the lagerphone very much now, although I'm trying to subvert the folk scene in South Carolina by sending detailed construction notes to some friends there. When I used to play it I had rather an energetic style and, even though I used a steel washer between the crown seal and the screw head (so that the hole torn in the seal had to be at least 1/2" wide before it could fall off) seals lasted only about 3-4 gigs before needing replacement.

I was lucky enough to locate the manufacturers (which is how I know about the process and the sizing) and they were so stunned by my use of their seals that they were quite happy to give me a box of them, which I still have. They were the old style (seal pressure-forced onto the bottle, rather than screw-threaded) but the tone was perfect all the same.

As an aside, the crown seals I found in America, while all with plastic inserts, came in (at least) two varieties. Most inserts were unable to be extracted intact, resulting in a dead tone useless for a lagerphone, but some inserts came out intact if you were careful; these were great,

An (expensive) alternative is to collect the curved steel disc that protects the traditional champagne cork from being cut by the wire twist that keeps the cork in the (high pressure) bottle. A collection of such discs would give a simialr tone to the crown seals but you'd be making a very different instrument, called a champerphone.

Cheers, Rowan