Hi there- thanks for posting!
It sounds like you are talking about a channel balance possibly. Could you send us over some photos of the balance removed from the window? This really will be the best way for us to determine the best recommendation option for you. Thanks so much!
I'm leaning toward the S385-27 balance. Can you verify a few things?
Is your shoe 1-3/32" (or so) as shown below? Is your metal channel 27 inches long? Does your sash weigh between 30 and 33 pounds? If you verify all that information, you can use the S385-27 with a "2660" stamp option. Up-to-date pricing is available via the links in my post.
I need the depth measurement of the shoe to finish confirming the recommendation. Measure from the back, near the clip, to the tip of the plastic on the front, as in the photo. It should be 1" or 1-3/32"-ish.
I'm not so sure about that. The metal channel looks to be 1/2" or so. If the metal channel is 1/2" thick, and the plastic sticks out further than the metal, it cannot measure a 1/2" itself. See your attachment here? What's the length of the green arrow? It's around 1".
Most Milgard windows with side-load balances use Series 385. This balance uses the 15-004 bottom balance shoe (1-3/32" depth). Your shoe might have worn down from being used, I think. Your safest bet is to order the S385-27 balance. The spring weight for "26-6" will be our "2660" for a sash weighing between 30 and 33 pounds.
