International 1310 Back Up Light Bulb Size

The International 1310 back up light uses bulb size P21W or 199 depending on the specific application. Data for the listed components covers the range from 1971 to 1973.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1973	P21W
1971-1972	199 (Light Duty)

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 21W.	199

Other Locations

Additional Notes

The International 1310 backup light specifications cover model years 1971-1973, with two distinct bulb types appearing across those years.
The 1973 International 1310 uses a P21W bulb, while the 1971-1972 model years in Light Duty configuration use a 199 bulb.
Both the P21W and 199 are single-filament bulbs rated at 12V and 21W, making them electrically equivalent to one another.
Both bulb types share the BA15s bayonet base, a single-contact base design where the "s" denotes a single pin offset to one side of the base.
The P21W follows the ECE standard, a regulatory framework used in Europe and internationally, while the 199 follows the ANSI standard used in the United States and Canada.
The 199 is a variant of the widely available 1156 bulb, meaning the two share the same base and electrical characteristics under different catalog designations.
Because the P21W and 199 share the same base type and wattage, physical interchangeability between the two is technically possible, though their differing regulatory standards may be relevant depending on the market or application context.