replacement coil spring balances

A home owner from Somerville, MA says:
I'm seeking replacement balance parts for four windows. I can't find any identifying information on the windows themselves.

One window is 16 pounds and has the hardware shown in the first two photos. The number on the coil is 540.

Three windows are 11 pounds and have the hardware of the last three photos. The number on the coil is c5.

Should I put in two new coils per shoe? The shoe in the first photo had a coil screwed into each side, one of which was broken. The shoe in the fourth photo had only one coil screwed into it, and it seems to have broken relatively quickly - I don't know if it was done correctly before. So I'm not sure how many coils are appropriate - I just want to order them and have a handyman replace them. Thanks!
User submitted photos of a coil window balance.
Profile picture of Tom
Tom from SWISCO responded:
Thank you for posting. These shoes look like our 15-180. Do you agree? If so, check out our Series 190 coil spring, as well.
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