NOCKTURNAL SHIFT UNIVERSAL EASY OFF NOCK SYSTEM STROBING RED/GREEN 2 PK. Nockturnal Shift FIT lighted nocks features a convenient string-activated switch that illuminates immediately when the string is released and an external switch for easy shut off. These nocks feature 20+ hours of battery life and a durable design that is built to last. These nocks include bushings to fit X, H, S, and GT arrows. Each nock in this package weighs approximately 25 grains.