Hello there. This looks like a 15-111 Pivot Shoe. This shoe works with either our 1/2" thick Series 160 Coil Springs or 3/8" thick Series 165 springs. You will need to remove the springs from the window to get this measurement accurately. Also look for stamps on the actual springs themselves. If there are none, give us the exact weight of the window sash that these coil balances support. See the video below which shows how to remove and replace this type of system.
If the shoe is in good condition then it can be reused, but if you replace even one spring then you should replace all of them. You never want to mix old and new springs, but you can reuse undamaged plastic components without issue.
I don't think I've ever seen a 16 pound coil for any size spring. That's extraordinarily strong. Can you confirm that this is the weight printed on the spring? A better way might be to get the sash weight instead. If you divide the sash weight by how many springs you have, you can determine the proper spring calibration that way.
