S2 rims should be marked "Schwinn Tubular S-2". On some, the stamping is very light. On repainted rims, the paint can hide the stamping. S7 rims have one row of knurling. S2 rims have a double set of knurling. You can always tell Schwinn rims by looking at the inner part where the tube goes. The metal is folded over double and there is a seam right down the middle where the rim strip goes. Gary