Window sash

Thanks for posting. Just to clarify, these are called channel balances. The window sash is the moveable part of the frame with glass that these balances regulate the movement of. Don't worry too much about the inner configuration of the spring; in this particular case, that just comes down to different versions of this balance. In the past you have ordered the S380-29; assuming these are from the same house, then this is very likely what you need again. Just make sure the depth of the bottom nylon shoe, or the measurement from 'heel' to 'toe', is 1". Let me know if it differs at all. See the diagram below for reference. As far as the stamp option to select, 28F likely conforms to our stamp option of 2860, which means this balance can support a window sash in the weight range of 32 through 35 pounds. Let me know if you have any questions.

Comparison of the S380 and S385 balance shoes.

If you want to be extra-safe, weigh the window sash; placing it on a bathroom scale should suffice. The 2860 stamp designates a balance that can support a window sash in the weight range of 32 through 35 pounds. If your sash falls in that range, you'll be good to go; let us know if it does not.