The Gapper® is designed to take up the gap between your finger and the 3rd valve slide ring. The size Gapper® each player prefers depends on a variety of factors: brand of instrument, taper of finger, etc. However, most players find that, with Bach instruments, the size of Gapper® corresponds with ring size in roughly the following way: XS - 5; S - 6; M - 7; ML - 8; L - 9; XL - 10.
