The gentle jaw comes in three sizes, which are small, medium, and large. The small ranges from 22 mm to 32 mm. The medium ranges from 33 mm to 43 mm. The large ranges from 44 mm to 54 mm. Since the normal range of motion of a jaw is between 40 mm and 60 mm, some users will only need the medium and they will never use the large. Also, most people will never need the small size. However, we include all three sizes for your convenience since everyone is different.