The GMC M300 front and rear side marker bulbs both utilize a 63 bulb size across all configurations. The replacement chart covers 1954 to 1955 model production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC M300 uses the 63 bulb in both the front and rear side marker positions across the 1954-1955 model years.
The 63 bulb is an ANSI-standardized type recognized in both the United States and Canada, indicating a common North American fitment standard for the era.
This bulb operates on a 12-volt electrical system, consistent with the 12V automotive standard that became widespread in the mid-1950s.
At 0.63 watts, the 63 bulb draws very low power, reflecting its role as a marker light rather than a primary illumination source.
The 63 bulb uses a BA9s base, a miniature bayonet-style single-contact base commonly found in low-wattage indicator and marker applications.
The single-filament construction of the 63 bulb means it serves one lighting function only, with no provision for dual-intensity operation such as combined marker and turn signal use.
The front and rear side marker positions on the GMC M300 share the same bulb type, meaning a single bulb specification covers all four side marker sockets on the vehicle.