Help identifying window balance

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 S378, S380 and S385 balance shoes.