Blue shooter/plunger inner spring used on some DE/Sega/Stern machines.
Can also be used on Williams/Bally machines.
DE/Sega/Stern #266-5001-05.
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)