Coil balance

Hi there!

The pivot shoe shown here looks like the 15-191. This is designed to use the Series 160 coil balances. You'll have to check the coil spring's tongue for a stamped weight code. 

Let us know if you have any questions!

There ought to be a stamp printed on the spring's tongue. You can also indeed weigh the window sash and then divide the weight by the total number of springs in the window to determine the proper spring weights. 

Since the spring is stamped #6.5, you'd want the S160-06 6.5-pound spring. 

You'll notice two holes at the top of the 15-111 pivot shoe. This hole is bisected by a slot that the tip of the S160 spring fits into flat ways, then twists in the round hole to lock in place. I hope this helps. 

If the pivot shoe and springs are in good shape, you can reuse them. The coil spring support appears to be damaged though, so you'll need the 15-150D double spring support.