Needing Tension for YKK Windows - Has Number 9 on it

Thanks for writing in. This looks like an older version of the Series 140 Coil Balance system. Now, the only issue is I'm not sure if that stamp reads '6' or '9'; it's honestly tough to tell, and it's a shame the manufacturers didn't take that into account! A quick solution is to weigh the window sash that these coil balances support. Let me know what that exact weight is, and we should be able to tell you which spring weight you need.