stamp otion 27-d-40, series 770, but length is 28", which option do i pick on this site?

Question

Okay,so what i have is 4 series 770 balance rods, all with the stamp option on the existing rods being: 27-D-40, and the length of the metal only part of the rod (metal tip to metal tip) is 28". So, i don't know which ones i need to order as the length is 28" but stamp shows 27-d-40? please help me fig. which to order ?

User submitted photos of a window balance.

Tom · Accepted Answer

It's likely you have an old stamp that is no longer used by the manufacturer. I think your best bet would be to weigh your sash and refer to the chart we show on the S770-28 store page. That will tell you for sure what you need.