This is a Series 159 stainless steel spring for tilt windows. It moderates the operation of your window sash using a specifically calibrated coil spring that allows the window to stay open when raised and remain shut when closed.
Individually, this coil balance can hold 11-1/2 pounds. This is added together with the other coils to support the whole weight of the sash.
The weight you need should be indicated as a stamp or imprint on your old spring.
Measures 3/4" thick.
The maximum travel length is 40".
Designed to work with a pivot shoe (sold separately).
This coil balance spring is sold individually, not in sets.
Can work for either the left or right side of the window interchangeably.
Coil balances are also known as constant force window balances.