I bought the 7-8 and they fit perfectly. First thing to know about this mask - the S/M runs small. I spent over $40 for this item and the microphone no longer works. Eight months later Im about to fit the third pair of these that are provided in the pack. 23???????????????????23???????24????????????????????????????????????????????24?????????? It sounds superior when hanging. My husband has problems with his arches and these are very comfortable for him. Super easy to use! YOU MUST USE BOTH WRENCHES TO TIGHTEN - HOLD THE PEDAL IN PLACE WITH ONE AND USE THE SECOND TO TIGHTEN THE NUT so the wrenches are working opposite and against each otherDisappointed to date. In the picture, the main issue is the inner strap, since it cannot be tightened.