Light Sockets

I've been learning a lot about recessed lights lately. We've had some replaced and we're having a few more replaced shortly. I wanted to tell my electrician that I wanted something with a standard size light socket, but I didn't know the technical name for that. Today, I happened upon the Edison screw Wikipedia page. Apparently, there are only a few standard U.S. socket sizes: E12 (candelabra), E17 (intermediate), E26 (standard), and E39 (mogul). The E26 is far-and-away the most common size. E12 and E17 are used in specialty fixtures and E39 is used for street lamps and other high-output lamps that you're unlikely to find around a home. My electrician said that the RL trim will fit a PAR30, which is a flood-light size---the E26 is such a common socket that he didn't even think I'd be asking about it.