The GMC PM253 uses a 63 bulb size for both front and rear side marker positions. The replacement chart covers 1952 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 bulb size 63 is an ANSI-standardized type recognized across the United States and Canada, making it a regulated specification within North American automotive lighting standards.
The GMC PM253 uses the size 63 bulb for both front and rear side marker positions across the 1952-1955 model years.
The size 63 bulb operates on a 12-volt electrical system, consistent with the standard automotive DC voltage used in vehicles of that era.
At 0.63 watts, the size 63 bulb draws a very low amount of power, which is characteristic of small indicator and marker lamps rather than primary lighting sources.
The size 63 bulb uses a BA9s base, a miniature bayonet-style fitting with a 9mm collar width and a single pin, which physically distinguishes it from other bayonet base types such as the BA15s.
The single-filament construction of the size 63 bulb means it serves only one lighting function per socket, with no provision for dual-intensity operation such as combined running and brake light behavior.
Because the same bulb size applies to both the front and rear side marker sockets on the GMC PM253, a single bulb type covers all side marker positions on the vehicle.