Adjustable rheostat control sight light with a purple LED light will increase your effective range by 20 plus yards. The knob control allows you to change brightness from low to high intensity. Works for both right or left hand models. Reduces pin glare at dawn and dusk. Batteries included. Fits sizes 1/4"-28, 3/8"-32, 3/8"-36, 7/16"-30 thread sizes.