need help identifying this channel balance

Question

1. The U-shaped metal channel is measured 21" long (metal to metal edges) x 5/8" (width of the opening) x 9/16" (depth)
2. The weight of the lower/movable panel of the single hung vinyl window (without the 2 balances) is 13.2#
3. Attached photos include the balances' entire front and back views, front, back,side and top views of the two ends with plastic guides
4. No stamp is found at the back or side of the channel, but there is a teeth-like mark close to one end of the channel (1" from the metal end, as in picture #3)
I'm looking for your advise of the replacement part identification, cost including shipping

Bob · Accepted Answer

Thanks for writing in. If the metal channel, not including the nylon fittings at either end, is 21" long, then you have either our S351-21 or S390-21. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the image below for reference. Measure the depth of your balance's shoe to determine which Series matches what you need.

Comparison of the S351 and S390 balance shoes.

If the window weighs just over 13 pounds, then choose a stamp option of 2030. This will support a window sash in the weight range of 12 through 15 pounds. Let me know if you have any other questions.