Channel Balances Non-Tilt Window 1/2" Width/ what model do I need?

A quick learner from Boyonton Beach, FL says:
Hello,

could u pls advise me what Series of Channel Balances show I buy? length of the metal channel is 31". also the current channel is marked with 30DS 38BSI VO

Tnx
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Emily from SWISCO responded:

Thank you for reaching out to us. We can help but this would have to be a custom order due to the 30DS38 stamp. It looks like you have our Series 380 or Series 385 channel balance. The vital difference between these two parts is the depth of the bottom shoe, as shown in the image below. Can you tell me which is the better match? Can you also confirm the number of balances you're looking to purchase? I can draft a price quote once we have those details.

Comparison of the S380 and S385 balance shoes.
Comparison of the S380 and S385 balance shoes.

A quick learner from Boyonton Beach, FL says:
Emily, tnx a lot for your prompt reply. I measured the plastic bottom, looks like it 1" and it's 15-005. I'm going to replace all channel balances in my house.
4 X 30DS38
2 X 36DS45 almost 37"
6 X 3850 almost 37"
6 X 3040 almost 31"
any idea why 36DS45 and 3850 have the same length?

tnx
Anton
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Emily from SWISCO responded:

Thanks for getting back to me, Anton! It actually looks like this won't need to be a custom order. My apologies! 

The 38 in your 30DS38 stamp represents the weight of the sash so you could use our stock S380-31 balance with the 3070 spring strength option. A pair of balances with this stamp will support a sash weighing 35 to 42 pounds. 

The same would go for the 45 in your 36DS45 stamp. You can use the stock S380-37 balance with the 3670 strength option. A pair of balances with this stamp will support a sash weighing 42 to 45 pounds. You can place an order for these parts directly on our website at your convenience. 

The metal channel for the 36DS45 stamped balance should measure 37" long, and the 3850 stamped balance's metal channel should be 39" long. The balance with the 3040 stamp should also measure 31" long. When determining length, you only want to measure the metal channel. 

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