Request to identify the balancer

Thanks for posting. This looks like a 15-087 Pivot Shoe. It works with Series 180 Coil Balance springs sold separately. For each replacement coil spring you have to choose a spring weight, which denotes the weight that individual spring can support. That '8' stamped on the shoe might indicate you need the S180-08 8 pound spring. However, it looks like there might be 2 springs on each side of the sash so I am not certain of this. Weighing the sash to find out exactly what you need would be best. See the video below.