A-shaped bulbs are one of the most popular bulbs used in the home. They are so popular the A-shape is probably what comes to mind when someone says light bulb. To tell the difference between one A-shaped bulb and another, the bulbs are classified based on their diameter.

 

A-shaped bulbs are recognized by their traditional pear shape. Since they are used so widely, most A-type bulbs have a medium screw base. This base simply twists into the fixture where the bulb is used. Some A-type bulbs also have European medium screw bases, and twist and lock bases.