window channel balance

I am trying to order the correct window channel balances for my single-hung, tilting windows. The channel balance is stamped 34D and measures 34" x 1/2" x 1/2". I can see balances that look the same, but the pivot ends look very different from ours. Can you help? I will need two of this size balance and also one 28D and two 28C balances.
Thanks for your assistance.

The pivot end of my balance was disassembled in my previous picture. Here it is assembled (both sides).

So do I purchase a S795-28 balance to replace both the 28C and 28D balances I need to replace? I was told the C and D indicate different spring strengths.

Can you buy just the pulley/spring holder piece versus the whole balance? This is the only part that is broken on many of our balance assemblies.