trying to determine between 390 and 351

A handy person from Los Angeles says:
October 14, 2021
I am trying to determine if I have the 390 or 351 type ballast. The actual measurement of the shoe is 1-1/16". Which one should I go with? I assume the 15 4 marking means 15# 4 ounces for the spring.
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Casey from SWISCO responded:
October 19, 2021

Hello,

As long as the depth of the bottom shoe measures over 1", you should be able to use the S390-16 channel balance with a 1540 strength option since the bottom fitting can wear down a bit over time from rubbing on the window jamb. Thank you!
16" Series 351 Channel Balance
16" Series 351 Channel Balance
S351-16
$9.34
16" Series 390 Channel Balance
16" Series 390 Channel Balance
S390-16
$9.34
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