Milgard single hung balance

Thanks for your photos. Based on what I see here, you have either our S380-27, S385-27, or S378-27 depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match.

Comparison of the S378, S380 and S385 balance shoes.

Odds are the plastic wore down a little over time. That's pretty common. With that in mind I think the 1-3/32" version is probably what you had originally.