Difference between S170-407 and S170-408?

A home owner from Illinois says:
April 16, 2015
I need to replace a few parts on a window. I do not have the exact model or series of the window. The pictures are helpful. What is the diference between the S170-407 and S170-408 coil spring?
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Paul from SWISCO responded:
April 16, 2015
Great, glad we can help. To answer your question, a single S170-407 coil spring can carry 7 pounds, while a single S170-408 coil spring can carry 8 pounds.
407 Series 170 Coiled Balance Spring
407 Series 170 Coiled Balance Spring
S170-407
$6.55
408 Series 170 Coiled Balance Spring
408 Series 170 Coiled Balance Spring
S170-408
$6.55
SWISCO S170 and S171 Coil Balance Assembly
SWISCO S170 and S171 Coil Balance Assembly
VIDEO
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How to Replace a Triple Coil Balance System
How to Replace a Triple Coil Balance System
VIDEO
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Removing a Triple Coil Window Balance
Removing a Triple Coil Window Balance
GUIDE
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