coil replacement needed

A home owner from Montreal says:
Hi,
This is part one of two posts. These photos are from the upper window. I have found the identical parts on your website. Unfortunately I don't see any information about the coils on the existing ones. It's a 1/3 - 2/3 set-up, with the bottom window (2+2 coils) weighing 20.4 lbs and the top (1+1 coils) weighing 10.8 lbs. Could you let me know which coils I should order?
Also, is the pivot shoe 15-191 (heavy duty)more durable that the 15-111 or is there another difference.
Which would you recommend?
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Tom from SWISCO responded:

Thanks for contacting us. So, if I'm understanding your post, your bottom sash has four springs supporting it (two on each side) and weighs 20.4 pounds, while the top sash has 2 springs supporting it (one on each side) and weighs 10.8 pounds.

That's easy enough to figure out. The next step after you have that information is to just divide the weight by how many springs support it. Can you just confirm the thickness of the spring? It looks like our 1/2" thick Series 160. Assuming I'm right, the bottom sash would use one S160-4 and one S160-5 on each side (4.5 lbs + 5.5 lbs = 10 lbs, 10 lbs x 2 = 20 lbs) and the top sash would use one S160-5 on each side (5.5 lbs x 2 = 11 lbs). 

The 15-191 is considered more durable than the 15-111. That's why it's labelled "heavy duty."

A home owner from Montreal says:
Perfect. Thank you. That is exactly the info I need. The coils are 1/2 inch and you interpreted my explanations correctly. I will place my order immediately.
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Tom from SWISCO responded:

Sounds great. We are happy to have been able to help you get pointed down the right path to the replacements you need. 

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