Sash balance broken

This appears to be a channel balance for a tilt window. We can help, but we need more information to narrow this down. I need you to raise and tilt the sash inward, then show us a picture of whatever clip is at the end of that cord that fits into the pivot shoe. We also need the length of the metal channel, as well as any stamp on the channel. We'll do our best to narrow this down from there.

Thank you for your patience as we looked into this for you. We are getting closer. You have a 34" channel balance with a 15-014 knife shoe and stamp option of 33TG. Now how does the balance attached at the top of the window track? Please show us a photo. From there we should be able to narrow this down. 

Thank you for getting back to us. You need a 34" Series 770 balance with a 15-014 Knife Shoe attached. We can provide this for you via custom order. I believe you will need these balances stamped 34E, which simply means they can support a window sash in the weight range of 32 through 34 pounds. I advise weighing your window sash just to make sure this range is correct; let us know if your window falls outside that range. If the stamp is correct, see the email Bob has just sent you to order a pair of these balances to those exact specifications. 

As far as the broken screw, if you can remove the threaded sash, good. If not, you will need to drill a new hole, either just above or below the old hole. 

Thanks for the response. I'm glad you checked the exact sash weight, as 34E would definitely be too strong--you'd have trouble closing the window and keeping it closed! Instead you'll need balances stamped 34D, which reflect a calibration for 27 through 32 pounds. I just sent you an updated purchase link for two of these balances. Let me know if you have further questions.