Window balance spring ID assistance needed

Question

Hello,
I am trying to identify a window balance spring so I can replace. Can you please assist me.

Metal portion of this spring is 29". Depth and Width are both 1/2".

The spring supports a non tilting window sash that is 48 inches wide and 30 inches tall(very heavy).

Stamping on this window balance spring is 28F.

Attached are three photos, please let me know if I can give you any more information. I would like to order two of these and have them shipped to me ASAP.

Thank you in advance!

Jasmine · Accepted Answer

Thanks for writing in! It looks like you have either the S380-29 with a 1" shoe or the S385-29 with a 1-3/32" shoe. Although, it does look like you may possible have a shoe with a depth of 7/8".

To determine which series is needed for your window, look over the dimensions from the diagram below to confirm the depth of your bottom shoe. If you do have a 7/8" please let me know, as this will need to be a custom assembly.

Since your balance is stamped with a 28F, the stamp will likely need to be our 2860 stamp, which can support a sash weight of 32 to 35lbs.

Comparison of the S378, S380 and S385 balance shoes.