Ligature for Rico Royal graftonite bari sax mouthpiece

I have a Rico Royal graftonite baritone sax mouthpiece. It is smaller in diameter than a regular hard rubber mouthpiece, so standard baritone ligature is too big and tenor sax ligature is too small. Does anybody know if Vandoren Optimum Ligature for Baritone sax will work? If not, I'm open to any other suggestion.

Rovner tenor ligature works fine on mine.

A standard tenor sax ligature should work on RR bari MPs. I have done this several times.

I don't have the RR bari mouthpiece, but I have had trouble finding a ligature to fit my bari mouthpieces ( a Morgan 1C, which requires a bass ligature, and a Selmer S-90 that is just slightly too small for the Selmer metal bari ligature). I've found that a flexible ligature like the Rovner or the B&G is more adjustable to size than a metal ligature.

If you want a metal ligature, AFAIK you will have to try them out (sorry, can't help with info about the Vandoren lig). They definitely have different sizes according to brand. If the size mismatch is not too large, you can use a ligature that is too large and increase the size of the mouthpiece by putting adhesive tape on the mouthpiece where the ligature touches. Don't wrap it all the way around (over the reed table), but just on the top and side. Black plastic tape is almost unnoticeable on a black rubber mouthpiece, and will last a long time.

I second the vote on the Vandoren Optimum - try it out at a shop. Most horn/sax shops will gladly let you bring in the mouthpiece to try out ligatures on it until you find the one that fits and sounds just right.

I have an alto Vandoren Optimum, and it doesn't fit all of my alto mouthpieces, so I wouldn't be surprised if you had trouble applying it here.