My ceiling fan has an unusual size fixture. It's larger than candelabra, but smaller than a standard medium. I suspect it might be intermediate, but I'm not quite willing to buy a converter with a huge shipping cost until I can get it confirmed. The brand is Hampton Bay. The fixture has a number E307185. Bonus points if you can find a method to convert the light bulb to a standard medium light bulb.
That's an intermediate base. I found them on Amazon. http://www.amazon.com/Watt-Light-Bulb-Intermediate-Clear/dp/B000QUXZTC