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I'm using a JK 6D on my BB flat contra. The rim is nice and I would like to order a JK for my Boosey E flat tuba. Although JK sizes are listed online, I have no way to know who the cup depths compare with mouthpieces that are more common in the US. For example which JK cup would be as deep as a Helleberg 7B? which one would be as deep as a 24AW? Which would be as deep as the large Helleberg or as shallow as a Wick 3SL? Thank you for your help.

It's a good question, and not answered by either of the references cited above as far as I can see.

All I have is a couple of large shank trombone mouthpieces, which is kind of slender information even for that, let alone the tuba series. But, if it helps,

1) when they say "extremely deep", "very deep", I would dilute that terminology a little before drinking - I doubt their "extremely deep" mouthpiece is really out of the ordinary, and

2) I have a hunch that the letter notation is absolute, not relative - that is, your 1A may not be any deeper than your 5A.

Note that these two observations are not internally consistent. If (2) is true, then the T5A probably is "very deep", for a 32mm diameter cup. But the 34mm T1A isn't - QED. I don't know, anyway it doesn't really add up, and it's possible that both observations are off the mark.

Thanks for the replies, I would like to be able to order a 6 rim with a cup like a 24 aw for general playing and also one with a little shallower cup like a 7B or Conn 2 for when more color is desired. I can tell you that the 6D I have has a cup about as deep as a Schilke 60 bass trombone mouthpiece but of course with a much bigger rim, and seems to be suited for contra bass trombone (mine also has the 12.5 shank which is bass trombone sized)

Hi - I think part of the problem is that the "depth" of the mouthpiece is something almost impossible to quantify other than relative to another mouthpiece of similar internal shape. The 24AW and the Helleberg are very different internal shapes. Dealing with curved surfaces leaves us unable to measure depth without some kind of standardized datum line - which still wouldn't answer how that particular mouthpiece plays when compared to another of differing shape, even if it measured at that same datum point. I'm not an expert on mouthpieces, and the best I can suggest is that you can't really extrapolate playing characteristics across makers, brands, or shapes.

It's convenient that you're OK with the rim size with the mouthpiece you already have in front of you; if only you had any numbers on depth, you could more or less complete the picture. Though I guess in principle the profile of the deeper cups in the series would still be a mystery, but I have a hunch they wouldn't be too straight-sided, judging from the trombone profiles. Is yours distinctly bowl or funnel shaped, would you say?

Anyway, if I were going to throw my money down on this quest, I might get the T6A and then decide on the second one based on what you see there. Rationale for choosing that over the T6AA: the A bore is already 8.4mm, which I think is plenty big; 6AA is at the margin of the chart, so potentially an extreme that's useful for the smallest minority. (I mean, apparently there's no T5AA.)

Anyway, whatever you end up with, I hope you'll let us know how they look! My trombone mouthpieces are great, very solid plating and good playing.

I think I've found something helpful. Doug Elliott's website has mouthpiece comparison charts, and they compare depth as well as diameter. And they list JK Mpcs. According to his charts, the JK A cup is about as deep as the 24AW or large Conn Helleberg. The B cup is about as deep as a Conn 2 or Heleberg 7B. So it looks like a Jk 6A or 6B is a good place to start!