Window block and tackle

Hello!

Can you confirm if your top fitting has wings or not? It's hard to tell from this angle. If it is indeed winged, you could have either the S380-29 or S385-29 channel balance. You'll need to measure as shown below. The S380 has a 1" bottom fitting and the S385 has a 1-3/32" fitting. 

Your "28D" stamp may correspond to our 2840 spring strength option, but you can weigh your sash to be 100% sure. There's a chart under the product description on the S380-29 and S385-29 store page that will show you which option you'll need based on the weight of your sash.  

Let me know if you have any questions!

Comparison of the S378, S380 and S385 balance shoes.