GMC F370 front and rear side marker bulbs utilize a 63 size across both positions. The replacement chart covers 1951 through 1955 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 F370 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 American National Standards Institute classification system used in the United States and Canada.
As a single-filament bulb, the 63 serves one lighting function only, with no secondary filament for an additional mode such as braking or running light.
The 63 bulb uses a BA9s base, a miniature bayonet fitting with a 9mm collar and a single locating pin, common in low-wattage indicator and marker applications.
The 63 bulb operates at 12 volts, consistent with the 12V electrical systems standard in automotive applications of this era.
At 0.63 watts, the 63 bulb draws very low current, reflecting its role as a marker light rather than a primary illumination source.
The shared bulb specification across both front and rear side marker positions on the GMC F370 means a single bulb type serves all four side marker sockets on the vehicle.