1620 is stamped on front side of channel.

A quick learner from Florida says:
Thinking the S390-17 is the one??. Your thoughts?
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Casey from SWISCO responded:


You very well could need the S390-17 as long as your bottom attachment has the same 1-1/8" depth as shown below. If not, I'd recommend you take a look at our S351-17 with a 1" bottom attachment. For wither balance, you'll need a 1620 spring strength option for your replacement based on your balance stamp. Thank you!

Measurements of 15-001 bottom balance attachment.
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