2950 BS7 sash window channel balance

Hi there, we're happy to give you a hand on this one. It appears you either have an S380-30 or an S385-30. They're basically identical except for the depth of the bottom plastic shoe. You'll need to measure yours to determine which is the correct balance for you. For either balance, you'll go for the 2950 option to match the stamp you mentioned. Let us know if you have any additional questions.

Comparison of 15-004 and 15-005

Yes, you are measuring the depth of the bottom balance shoe correctly. It's pretty common to see the shoes wear down over time and use. Since your shoe has worn down from 1", you can use our S380-30 sideload balance with a spring weight (2950).