Window Channel Balance Identification

A quick learner from USA says:
I believe these are series 770 channel balances and just wanted to confirm before I order. Thanks, I have 2 size one measures 35" long and the other is 29". The 35" ones are stamped 3500 and the 29" ones are stamped 2900. Both have a BSI stamp on them. I have several different size windows and have weighed all of the sashes.

for the 3500 I have 1 - 27lb window and 4 - 21lb windows
for the 2900 I have 1 - 24lb window, 2 - 18lb windows and 1 - 15 lb window
User submitted photos of a window balance.
Profile picture of Paul
Paul from SWISCO responded:
Thank you for contacting us. For all balances shown in your pictures, I recommend our Series 770 channel balance. Carefully look over this Series for each length you need and see if this is the appropriate match.
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