Window Sash Balance Spring replacement "28 3 Caldwell JM"

Question

Can you assist me in finding the correct replacement window sash balance spring part?
House built in 1994 in California, I assume original windows and springs.
Metal Channel is 5/8" wide on the open side and 29" long.
Metal Channels have stamped "28 3 CALDWELL JM"
I have one more picture of the window channel engagement block but reached the maximum allowed pictures on your submittal form.

Bob · Accepted Answer

Thanks for posting. This looks like it might be either the S351-29 or S390-29 Channel Balance. The only difference between the two balances is the 'depth' of the bottom nylon shoe, or the 'heel-to-toe' measurement. See below. Measure your old balance's shoe depth to see what matches best. For a stamp option choose 2830.

Comparison of the S351 and S390 balance shoes.