Window balance type
A handy person from Rockledge, Florida says:
December 30, 2013
I have a sliding 52 inch wide window x 30 inch high. The shoe and top are 7/8 inch wide that fits in the window slide channel. The metal balance is 30 inches long (metal part) and Marked BSI ME 2940. Another one of my windows is the same dimension but marked BSI ME 2930. I think I would rather choose the stronger 2940 weight model spring. the top depth is 1 inch. The shoe depth is 0.75 inch. Thanks.
Paul from SWISCO responded:
January 2, 2014
Thanks for posting. This balance appears similar to our S377-30. Check it out and let me know if you agree.
As for the balances marked 2930 and 2940, are they in two different windows? If so, you should stick with those same numbers. It's pretty important you get the exact stamp option you need. If it's too strong or too weak, the windows won't work well.
There is a list of stamp options under the S377-30 that also details how much sash weight each option can hold up. You should weigh each sash whose balances are being replaced to ensure you are getting the right option.