The bass and alto Clarinets can be fitted with the Maestro thumb rest only when there are no thumb keys for the lower notes!!!!!!

But even then I would advise something else!!!!
You never carry these instruments on your thumb so a thumb rest as the Forza for saxophone would do much better.

But again when there are no thumb keys........

Only the factories could make something better espcially for these instruments because there are too may differences to make something universal.

(I'd happily work together)