replacement block and tackle tensioners

A handy person from residential says:
I am replacing the broken balancers in my windows. They look like the 350 series. They are 29 inches long. They have stamped on them ub 26D USB and 28D USB. I was wanting to order the correct one. Thanks Jim
User submitted picture of channel balances.
Profile picture of Paul
Paul from SWISCO responded:
Thank you for posting, and for the pictures. Are these two balances both in different windows, or are they a single pair in a single window?
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