Replacement balance springs for single-hung window

Hello! I live in central Florida. The window in the spare bedroom was difficult to open, until my son forced it, and then it wouldn't open at all. I removed the balance springs, which appeared to be rusty, and observed that the "ear" on one of the plastic shoes was broken off. I need to order two replacement balance springs, but after looking at your selections, cannot determine which ones are required. My balance springs appear to be 17 inches long X 1/2 wide. Stamped on each spring lengthwise is 16 9, followed by "PL" in a much smaller font, followed by "BSI" stamped sideways. I cannot determine the window manufacturer. A "FMA Keystone" label is on the window, but I think that's a measure of impact resistance. (I live in hurricane country) Thanks for your assistance.

Hi, Tom and thanks for the quick reply! I looked at the measurements for the two bottom shoes and then measure mine. I don't have a micrometer, and my steel ruler is only graduated into 16ths, (and I don't know if I could even SEE a 32nd of an inch) but my bottom show appears to be just a tad OVER 1 and 1/16 inch, so I think I need the S385-17. Is that correct? Thanks!

Hello. The replacement parts arrived in a timely manner, and I installed them after reviewing the video several times. The window now slides up and down freely, but won't stay open. I compared the old balance with the new balance, and they appear to be identical, except for the engraving. I removed the sash and weighed it (on a digital bathroom scale) and the sash appears to weigh 25 pounds. If I had to guess, I mistakenly ordered balance with a spring that's not heavy enough. Please tell me what part I need, and how I can exchange the ones I have. Thanks!

Hello. I ordered the series 385's and they arrived in a timely manner. I compared the old balance springs with the new ones and they appear identical, with the exception of different markings. After watching several YouTube videos, I installed the new balance springs, and everything was OK, EXCEPT the window won't stay open. I weighed the window sash on my digital bathroom scale, and it appears to weigh about 22.0 pounds. What did I do wrong, and how can I fix this? Thanks!