Coil balances 1/2" wide

A contractor from Wayland, MA says:
I'm trying to match these coil balances for a 20 to 25 year old window that weighs 12+ lbs. The number 6 is stamped on the coil but no other letters are visible. The coil is 1/2" wide, the pocket is 9/16" deep and around 1-1/2" wide. The coil has a hook on both ends which doesn't match your available coils so i could order new pivot shoes too if necessary.
Any help would be greatly appreciated.

A customer submitted photo of a coil balance.
Profile picture of Paul
Paul from SWISCO responded:
Thanks for posting, John.

Unfortunately, that was our Series 151 coil spring, and the manufacturer has discontinued this style. They suggest using the S152-6 Coil Balance as a replacement with the 15-158 Coil Balance Shoe. You might also need the 15-143 Coil Bushing, the 15-144 Coil Bushing Cap and the 15-145 Coil Support Barrel.
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