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LM-10 rim is basically the same as a Marcinkiewicz N4. I believe you'd find it to be more on the wide side compared to many mouthpieces out there, but not as wide as a C4. The LM-3 rim also works very well on the LM-10. In fact, that's the setup I'm using now. Makes a nice difference in clarity of articulations.

...D

I play with a C4 rim on my LM-10, but I have the original LM-10 (TJ) rim as well. I concur with Dave that the C4 rim is wider--it LOOKS like it's flatter, too, although that's subjective.

I haven't played on the LM-10 rim in years--for whatever reason it never worked for me, but the C4 rim did. I hope that helps.