SEAL TWISTOR helps to reduce the chance of installing damage. It turns seal to an omega shape so as to make the size of seal smaller than the gland diameter. Seal crosses over the sharp chamfers safely then rebounds in the groove. Four different sizes in a set: S(0.7"~1.187", 20~30mm), M(0.187"~2", 30~50mm), L(2"~2.75", 50~70mm), XL(2.75"~6.5", 70~165mm).