Thanks for posting! As stated on the S770-29's product page, the stamp option represents the strength of the channel balance. More often than not, you can locate the stamp on your channel balance. However, in your case, that does not seem to be the case.
Your best bet at this point is to weigh your window sash and compare its weight to each option for the
S770-29. The weight range for each option are as follows:
-29A: 7 through 12 pounds
-29B: 12 through 18 pounds
-29C: 18 through 23 pounds
-29D: 23 through 28 pounds
-29E: 28 through 32 pounds
Please keep in mind that the weight range information is based on 2 balances per sash. Balances are designed assuming frictioan in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
