believe these are 1977 because this is when house was built. not able to send photo. maybe when son gets home. dont know when that will be. numbers on balancer are j28 5#23 2-78 same side as stamp for anderson is on. other side 11600-3
Casey from SWISCO responded:
June 1, 2020
Hello,
Take a look at our 24-531 Andersen Sash Balance. This is meant to replace Andersen balance boxes that include the stamp 523, or 5#23. Thanks for posting!