Spiral Sash Balance Replacement

I have a 7.48 pound wooden sash that needs replacement balances. The tube length is 19 inches, measured diameter 9/16 inch. The color of the plastic at the base is indeterminate. What color series 500 balance should I order? I enclose a picture of the base end of my balance.

Thanks for the help!
Barrie

Thank you Paul. I ordered your recommended parts, they arrived fast, and I just finished installing them. The parts fit PERFECTLY, even to using the same screw holes. The window works smoothly again, and wife is ESPECIALLY happy not to need the stick to hold it up, and risk pinching her finger again. :-))

You ought to establish a relationship with the home supply stores like Home Depot & Lowe's so they can supply correct PARTS instead of recommending replacing the whole window. :-(

Nice job!! :-))

Best Regards,
Barrie