Each 2-Pack contains 2 size #21 Xact-Fit™ rings. The incredibly popular PlayZone has proven our revolutionary Xact-Fit™ 2.5mm (0.1) incremental cock ring sizing system is the most precise on the market. Super strong, but soft to the touch, Xact-Fit™ rings stretch just enough to get on and off, but otherwise should provide a very comfortable (no pulled pubes!) and effective fit. The sizing # references the ID in inches (#10 = 1.0 ID, #11=1.1 ID etc)All 14 Xact-Fit™ rings sizes are now available in single size 2-packs. 3 Ring Kits of M, L, XL and Mixed are also available.Don't know your size? We recommend you start with the Play Zone Kit, which features 9 incrementally sized Xact-Fit™ rings on a bright orange mini traffic cone.Each Xact-Fit ring is stamped with its size so no more guessing! Stack the rings for additional fun.