GMC 300 front and rear side marker bulbs utilize a 63 bulb size across both positions. The replacement chart covers 1951 to 1955 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC 300 uses the 63 bulb for both front and rear side marker positions across the 1951-1955 model years.
The 63 bulb follows the ANSI standard, which is the recognized classification system for automotive and miniature lamps in the United States and Canada.
This bulb operates on a 12-volt electrical system, consistent with the standard automotive voltage adopted broadly in mid-20th century vehicles.
At 0.63 watts, the 63 bulb draws a very low amount of power, reflecting its role as a marker lamp rather than a primary illumination source.
The 63 bulb uses a BA9s base, which is a miniature bayonet-style single-contact base with a 9mm collar width, commonly found in small indicator and marker applications.
The single-filament construction of the 63 bulb means it serves one lighting function only, with no secondary circuit for braking or turn signals built into the lamp itself.
The front and rear side marker positions on the GMC 300 (1951-1955) share an identical bulb specification, meaning the same 63 bulb fits all four marker sockets on the vehicle.