2) Maximum overall length (MOL) of the bulb is measured in inches from end-to-end. For example, this M400/U has an MOL of 11.5 inches.
3) A bulb's base is measured in millimeters. For example, this 35W 120V JDR halogen bulb has an E26 medium screw-in base, which measures 26mm in diameter.
4) A fluorescent bulb's base is measured from the center of one pin to the center of the other pin. For example, this G30T8 Germicidal Fluorescent Tube has a G13 bi-pin base, which measures 13mm from pin to pin.