Coil balance springs and shoes

I agree, the shoe looks like our 15-111. This shoe tends to use our Series 160 1/2" thick springs, but it also sometimes uses our Series 165 3/8" thick springs as well, so compare the thickness of your old coil springs to confirm what matches up. Let me know if you have further questions. 

The 5 stamp likely means these are 5 lb springs, or rather, they support 5 lbs of support individually. Again, depending on the thickness of your springs, that would mean you need either the S160-5 or S165-5. If you're uncertain about the spring weights you need, give me the exact weight of the window sash, and I can work it out for you.