This was a fairly late addition to their catalog - probably in the early 2010's - and so not many are in circulation. It is a copy of the Warburton 3FLM and their website describes it as a "medium funnel" and as having "a lighter sound and is preferred by players who need to play in the upper register". I would agree that the sound is lighter, but I generally frown upon a lot of upper register from a flugelhorn. The funnel shape of the cup is very appropriate for the flugel and will help keep a horn from sounding tubby.
Cup diameter is 0.670, which is like a 1 1/2C. Warburton makes theirs with a no. 20 throat, but the Kanstul version is a no. This modular cup is threaded and is compatible with cups produced by Kanstul as well as those made by Warburton, Legends Brass and James R New.
Kanstul did all of their plating in-house, using proprietary methods developed by Zig's son Mark Kanstul. This cup received a generous silver plate, and shows almost no wear. Favorite us, and check back as we are listing more interesting and exclusive mouthpieces!