C-9 Shaped Miniature Bulbs are miniature bulbs that are CONICAL in shape. The number following the letter C indicates the diameter of the glass CONE in eighths of an inch. C-9 Shaped Miniature Bulbs have a diameter of 9/8 or 1.125" which is 28.575 millimeters. C-9 Shaped Miniature Bulbs come with an Intermediate Screw Base (E17) configuration.