Coin spring broke
Hello there. This is a 15-180 Pivot Shoe, which uses Series 190 Coil Balances. Let me know if you have any other questions.
If your old stamp is faded off, or otherwise unreadable, then you will need to weigh your sash on a scale to get its weight. Then, divide that by how many springs support it in total. It looks like you only have one on each side so that makes it easy.
So, for example, if your sash is 10 pounds, you'd want one 5 pound spring per side. Hopefully that makes sense.
As for what the S190 stamps represent, that gets a little more complicated. Each stamp has 3 digits, as you can see, but you really only need to worry about the first one: that's the weight. So the 640 supports 6 pounds per spring, the 940 supports 9 pounds per spring, etc.
The second two digits are all "40," which indicates the travel of the spring. You don't have to worry about this unless your spring is for whatever reason installed higher than 40" from the sill, which is uncommon in modern windows. If that is the case for you, you'd simply install the balance lower to compensate.
I weighed my sash. It is 19.8lbs. But the maximum choice for S 190 at your store is 9lbs. Will it work? Any alternatives? Thanks.
A 10 pound spring would be perfect for that kind of weight, but that's unfortunately not something that we sell. With that in mind you will need to go with a lower weight, but more springs.
I recommend using two S190-540 springs per side. These carry 5 pounds each, so it should be able to hold up your sash with no problem.
The catch is that if you're using more springs, you need a way to retain them in your frame. You won't be able to use the same clip you have in your window now. Check out our 15-181 for my recommendation. You'll also need one 15-182 bushing per spring (you may already have some in your window now; these can be reused).