Mack Granite (GU) Dome Light Bulb Size

The Mack Granite (GU) dome light bulb uses a 561 size specification for this component. The replacement chart covers vehicle production years spanning 2011 to 2022.

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
2011-2022	561

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, 44mm length, end-cap contacts. 12V, 12W.	561

Other Locations

Additional Notes

The Mack Granite (GU) uses the 561 bulb for the dome light across all listed model years, spanning 2011-2022.
The 561 is a festoon-style bulb, meaning it is cylindrical in shape with metal end-cap contacts on each end rather than a base pin or wedge fitting.
Festoon bulbs are held in place by spring-loaded clips within the fixture, with the end caps making direct electrical contact at both terminals.
The 561 bulb has a physical length of 44mm, which is a critical fitment factor, as festoon bulbs must match the socket span precisely to seat correctly.
The 561 operates at 12 volts and 12 watts, consistent with standard 12V automotive electrical systems found in commercial trucks.
The 561 carries ANSI standardization recognized in both the United States and Canada, meaning the specification reflects a consistent, regulated designation across North American markets.
Because festoon bulbs are sized by length, a 561 replacement must match the 44mm specification; a festoon bulb of a different length will not make proper contact with the fixture clips.