The Lumenok X lights up instantly with shot inertia and stays lit, so you can track your arrow to your target and find it easily after dark. It glows for up to 40 hours or until switched off, and it only adds 16 grains to the total weight of your arrow. It replaces the nock of the ST Axis, ST Axis Obsession, Black Max MFX and MAX-4 MFX. Available: Single pack, Three pack. Color: Fluorescent Red.