TubeNet

I was looking at a vintage Conn catalog (1927 or so) and on page 19 there are the Bass tuba mouthpieces. Besides the Helleberg, the Chief, the Eb Monster, there is one marked "L" on the shank and on the page it says "LTD" model and it says it is a special mouthpiece. It has a narrow inner rim, with a shallow funnel. I have one and it works well on old Eb tubas with thick-metal bells that don't resonate with other mouthpieces.

Do you happen to know the intended use of this mouthpiece? (I wouldn't mind buying another one)

Thanks for any information. William