Channel balances identification

A quick learner from USA says:
I believe this is a Series 351 but I do not recognize the stamp.

Can you determine if this is correct or if it is a custom balance?
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Thumbnail of the uploaded file named 38-5
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Tom from SWISCO responded:

Thanks for your photos. Based on what I see here, you have either our S351-39 or S390-39, depending on the depth of the bottom shoe. That's the only difference between them. I recommend measuring your shoe and referring to our dimensions to confirm the best match. Looking at your fourth photo, the shoe looks to be over 1" deep, which makes me think it's the S390-39. Can you triple check that?

As for the stamp, 38-5 usually matches our 3850. This isn't a stock option for either balance, but it may still be something we can supply. For now, please verify the depth of that fitting and in the meantime I will check on the availability of the 3850.

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Tom from SWISCO responded:

Hello again! We just added the 3850 stamp as a standard option for both the S351-39 and S390-39. Just note that we don't currently have them in stock and anticipate a 5-6 week lead time before we are able to add any to our inventory. For now, you can select to be notified when they'll be available directly from either of the aforementioned store pages.

A quick learner from USA says:
So should I not use the 351? I measured again and it looks to be 1" - what is the difference between the 351 and 3850?
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Tom from SWISCO responded:

I'm not sure what 3850 is in this case. That's not one of our product numbers. As for what Series you need, that's not a decision I can make for you. All I can say is that looking at your photos, the shoe depth looks over 1". However it's admittedly difficult to make out such a precise measurement from just a photo of a tape measure. At the end of the day, you need to measure it as carefully as you can and use your best judgement.

A quick learner from USA says:
"We just added the 3850 stamp as a standard option for both the S351-39 and S390-39"

^^ that's what I am referencing for 3850.
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Tom from SWISCO responded:

Thanks for clarifying. The "3850" is a stamp used across many, many different balances, including the Series 351, Series 390, and many more. It's not a product code or anything. The only difference between the Series 351 balance and the 3850 stamp is that the Series 351 is a complete channel balance assembly, while the 3850 is a code that represents how strong the spring is.

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