Flashlight Tailcap Pressure Switch Tail Switch for Ultrafire 501a/501b/501c/501d/501n Flashlight Outdoor Living High quality of build with little or no roughness to the cap threads Threads on easily to an Ultrafire 501A/501B/501C/501D/501NPressure pad works well, and is held down easily by rubber bands Now you have a choice of constant-on light activation without having to rotate the tailcap of your light Click the adjustable pressure switch end button into constant-on mode, click again for off