Window Balance Part

Hey Chris. If the metal channel, not including the nylon fittings on either end, is 27" long, then I agree that this is likely an S385-27. The only other possibility is the S380-27, which is near identical, except the depth of the bottom nylon shoe is different. The shoe depth can be thought of as the 'heel-to-toe' measurement. See the diagram below for reference. Measure the depth of your existing balance shoe to see if either the Series 380 or Series 385 is right for you.

Comparison of the S378, S380 and S385 balance shoes.

You then have to choose a stamp option, which designates the balance's strength. Look for a stamp on the old metal channel that indicates this. If there is none or you are unsure, obtain the exact weight of the window sash. You can then match that exact weight with one of the weight ranges listed alongside each stamp option under the product description of either the S380-27 or S385-27 shop page.