when select the option, S1 means only buy sizing sound 5.5-10mm, S2 means only buy sizing sound 10.5-15mm, S1+S2 means both sizing sounds 5.5mm-10mm+10.5mm-15mm. E1 means E1 tetherspout kit without locking ring E1+locking ring means E1 tetherspout kit with locking ring. E2 means E2 tetherspout kit without locking ring E2+locking ring means E2 tetherspout kit with locking ring E3 means E3 tetherspout kit without locking ring E3+locking ring means E3 tetherspout kit with locking ring TetherSpout Device is desiged for someone who has chastity requirement but non-piercing.It can be used separately or used with cage. Want to know more about it,visit this link. http://tetheredchastity.blogspot.com Here are the two sizing Sounds/dilators that are available. 5.5mm-10mm 10.5mm-15mm To figure out which sound/dilator is best for you, try this suggestion: measure the vertical length of your slit while flaccid and without stretching it (the outside is elastic, unlike the inelastic part further inside). If it is at least 14mm (0.55") in length, get the 10.5mm-15mm sound. Otherwise, get the thinner 5.5mm-10mm sound. But it is always better to get both sizing sounds. Here are 3 existing combinations of TetherSpout. E1:as below length 28mm barrel diameter 6mm flange diameter 8mm 4 retaining rings' diameters 10mm and 11mm,12mm,13mm E2:as below length 28mm barrel diameter 7mm flange diameter 9mm 4 retaining rings' diameters 11mm and 12mm,13mm,14mm E3:as below length 28mm barrel diameter 8mm flange diameter 10mm 4 retaining rings' diameters 12mm and 13mm,14mm,15mm Tip: the screw is to "bite" the solid wall, not screw into the tether hole.No need to twist screw wrench with big force to bit the wall, when screw in the screw.You can stop when you feel the twist become a little tight.