Standard tension spring used on many Williams/Bally pinball machines.
Williams/Bally #10-148-1.
American Pinball #SPR0007-00.
Spring tension from lowest to highest:
Blue (266-5001-05)
Green (266-5001-04)
Standard (10-148-1)
Orange (266-5001-07)
Purple (266-5001)
Gray/Silver (266-5001-14)
Red (10-148-2)