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Hi there! You could either have an S380 or S385 channel balance. You’ll need to measure as shown below. The Series 380 has a 1" bottom attachment, and the Series 385 has a 1-3/32" attachment. You'll also need to remove and weigh your sash to choose the appropriate stamp option. There's a chart on the S380 and S385's product page that shows you which option you'll need based on the weight of your sash.

Comparison of the S378, S380 and S385 balance shoes.

You can find the prices for the Series 380 and Series 385 on their respective product pages. 

If you have any other questions just let us know!