Window non tilt out balance

Thanks for posting. This looks like it might be either an S351-36 or S390-36 Channel Balance. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the diagram below for reference. Compare both with your old hardware to see what matches best. For a stamp option choose 2540.

Comparison of the S351 and S390 balance shoes.

Great, I agree. If the depth is 1-1/16" then it was probably 1-1/8" originally and just wore down over the years. Happens all the time.

As for length, it's normal for a 36" balance to have a stamp whose first two digits start with 35". It's important to note that the stamp is not representative of the size in any way. To determine length, you always measure the metal channel and base your purchase on that dimension, not on anything printed on the hardware itself.