Help identifying window balance

A quick learner from Brainerd, MN says:
July 25, 2023
Metal channel is 20 inches long.
Writing on metal channel reads?

unique 19-D-40
30/10/99
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Emily from SWISCO responded:
July 26, 2023

Hello!

Your balance looks like either the S380-20 or S385-20 to me. You will have to measure as shown below to determine which Series is best. The 19-D-40 stamp may correspond to our 1940 stamp option but you can weigh the window sash on a scale to confirm. A pair of balances with this stamp can support a sash weighing 14 to 17 pounds.

Comparison of the S380 and S385 balance shoes.
Comparison of the S380 and S385 balance shoes.
20" Series 380 Channel Balance
20" Series 380 Channel Balance
S380-20
$9.38
20" Series 385 Channel Balance
20" Series 385 Channel Balance
S385-20
$9.38
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