15, 25, 50, 75. I don't know if the numbers correspond to any unit of measurement but regardless, the bigger the number the bigger the rubber and the tighter the glasses will fit. I don't think anything other than 15 and 25 is made anymore...which is practical because if you need a 50 or 75, the glasses are either mega loose or too big for your face

T-shocks 15, 25, 50, 75 are all the same except for their numbers and sku. 15 comes from pack of 15's, 25 from pack of 25's and so on. the number doesn't serve any purpose but identifier of which sku it comes from for inventory purposes.

I guess so, I'll try tomorrow. It's funny how they pack the spare t-shocks, usually we replaced t-shock both sides except for 50 all are odd numbers.

This is not correct. Each T shock number represents a different size rubber...the bigger the number, the bigger the rubber, the LESS the are arms open, the tighter the fit. They have EVERYTHING to do with fit as I noted in my original post above.