Bach K342 3C

I use this mouthpiece with the Thomann FH 600 G Flugelhorn - it doesn't fit so great as the shank of the mouthpiece is too narrow vs the wider lead pipe of the flugelhorn. But with a bit of protective tape on the mouthpiece it's ok.

It plays wonderfully easy, all the higher notes slot very well - like instantly adding a few years practice to your skill level. Intonation is better than any other mouthpiece I've tried.

The only downside is that the tone is a bit bright for my taste, would be nice if it was a bit darker/warmer, but it's ok, and definitely worth this compromise for the playing benefits.