The designation Exx refers to the base diameter in millimeters (i.e., E12 has a diameter of 12 mm.) This is distinct from the bulb glass size which in the U.S. is given in eighths of an inch (i.e., A19, MR16, T12).
Cassegrain reflector | Reflector sight | Parabolic reflector | reflector sight | Multifaceted reflector | Corner reflector |