These custom motorcycle STOP tail lights are a reproduction of the original made by Miller which appeared on HRD Vincent and Velocette motorcycles starting in 1947. It acts as a running light, brake light (STOP lights up when you brake) and it also features a clear lens to illuminate your license plate. 12 volt bulbs are included, you can also swap them out to 6 volt bulbs for older charging systems. The lens of this light measure 2 5/8" in diameter.