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Emily from SWISCO responded:
July 7, 2021
Hi there! It looks like you have either our S351-17, with a 15-002 bottom attachment, or S390-17, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. You'll also need a spring strength option of 1620. When measuring your balance make sure to only include the metal channel in your measurement. Your stamp is "1620" which means your metal channel should measure as 17". If you have any further questions just let us know. 
Comparison of the S351 and S390 balance shoes.
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Tom from SWISCO responded:
July 8, 2021
If the stamp on your balance is 1620 then the metal channel should be 17" long. I can't quite tell from the angle of your last photo what the length is for sure, but I highly recommend double checking that. Assuming that it is 16" long then that means that the installers cut it down by an inch before they put it in. It's uncommon but it does happen, they must have had a good reason for it. If that's the case then you can use our 16" balances but you will have to weigh your sash to determine the proper stamp option; all of the 16" balance stamp options start with a "15," so they would be 1510, 1520, 1530, etc. You may indeed need a 1520 but I wouldn't bet on it. You should weigh your sash to be sure. We have a chart on both the S351-16 and S390-16 store page that tells you exactly how much weight each option supports. |
