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This appears to be a Series 795 Channel Balance. I'd like to confirm a few more details. Please tell me the length of the metal channel. I need the exact weight of the window sash, to know what stamp option your new balances should use. Please show me how the balance attaches to the top of the jamb track; does it use a screw clip, or a hook instead? Finally, you need to determine which T-Lock Shoe your balance uses. Read more about modifying the Series 795 here.