The Home Depot lists more than 15 different types of light bulb bases, including medium, candelabra, medium skirted, bipin and twistline. Other base types include intermediate, mogul, widepin and candelabra bayonet. Each bulb base requires its own receptor on a light fixture.
Bases for general light bulbs usually come in screw types, while compact fluorescent bases are normally pin types. Larger fluorescent light bulbs most commonly use pins that attach to power sources. Halogen bases also use pin types. Some base types have alphanumeric designations rather than names, such as G-23, G24d-1 and GX23. These bases belong to compact fluorescent light bulbs that plug in to a power source instead of twisting.
Different base types may have varied widths and lengths. A candelabra base measures 0.470 inch wide and 0.65 inch long. Intermediate bases are 0.642 inch wide and 0.82 inch long. Medium bases, the type that most regular household bulbs use, measure 1.03 inches wide and 1.05 inches long. Mogul bases are 1.55 inches wide and 1.88 inches long.
Individuals order light bulbs with different bases from online sources or from local retailers, such as hardware stores, home improvement retailers, lighting specialty stores or national retailers with small home improvement sections. Customers can use online charts and illustrations to compare base types with their own bulbs.