Wider bore than the S-series, therefor a richer sound. Available in B-flat down to low G. (Note that the B-flat whistle is no longer available in the S-series.)
When ordering a set of one headjoint with multiple whistle bodies, or an extra whistle body, please specify the pitch(es) desired when you are asked to "Add Comments About Your Order".
Finger hole keys (Susato calls them "Comfort Keys") are available on all of the M-series whistles. They are also available on the L-series whistles, and are standard on the LX-series whistles. These keys make it more comfortable to reach and cover certain finger holes on the larger whistles, such as those covered by the ring fingers. You can see some comfort keys installed on the seven left-most whistle in the photo on this page.
When ordering just one key, please specify whether that key should be for the top or bottom hand ring finger when you are asked to "Add Comments About Your Order".