Windows wont stay open/closed

Question

So hopefully you can tell me the parts I need from the above pics. I have several windows in the house where the bottom won't stay in the lifted position and the top falls down if the window is not locked.
I'm sure its the counterweight/spring assembly on most, although I have seen a couple where the plastic cradle of the cam assembly is broken.
Do I need to replace both sides, top and bottom? How do I know?
I have 21 of these windows in my home. At least seven are malfunctioning. I'll probably need enough parts to do twelve (maybe I should have the parts to do them all?) windows as I expect more to fail over time.

Bob · Accepted Answer

This looks like our 15-192 Pivot Shoe. This shoe connects with Series 170 and Series 171 Coil Balances. These coil balances regulate the opening and closing of the window. To know which spring weights you need, look for stamp numbers on the springs. If there are none, or you are uncertain, obtain the exact weight of the window sash. Give me that exact weight and I can work out what you need.

You only need to replace the springs and balance parts that are damaged. The video below shows how to remove and replace a similar coil balance system.