A perfect fit in my big Maglite 6D cell flashlight.  Seems a bit brighter than the standard bulb that I removed.  It was easy to install.  The zoom/focus aspect of the orginal Maglite seems to work a little differently.  It goes from a very tight spot to a little wider spot with a dead spot in the middle.  I guess, for the most part, the LED replacement bulb defeats the zoom.