Mack MC Headlight Bulb Size

Mack MC headlight bulbs utilize H6024, H4651, and H5001 sizes for high beam applications, while low beam configurations require H6024, H4652, and H5006 bulb sizes. The replacement chart covers vehicle production spanning 1981 to 1991 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.

High Beam Headlight

Years	Bulb Size
1981-1991	H6024 (With 2 Round Headlamps)
	H4651 (With 4 Rectangular Headlamps)
	H5001 (With 4 Round Headlamps)

Low Beam Headlight

Years	Bulb Size
1991	H6024 (With 2 Round Headlamps)
	H4652 (With 4 Rectangular Headlamps)
	H5006 (With 4 Round Headlamps)
1989-1990	H6024 (With 2 Round Headlamps)
	H4656 (With 4 Rectangular Headlamps)
	H5006 (With 4 Round Headlamps)
1987-1988	H6024 (With 2 Round Headlamps)
	H4652 (With 4 Rectangular Headlamps)
	H5006 (With 4 Round Headlamps)
1982-1986	H6024 (With 2 Round Headlamps)
	H4656 (With 4 Rectangular Headlamps)
	H5006 (With 4 Round Headlamps)
1981	H6024 (With 2 Round Headlamps)
	H4652 (With 4 Rectangular Headlamps)
	H5006 (With 4 Round Headlamps)

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). 7-inch round sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H6024
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H4651
ANSI standard (US & Canada). 4-inch square sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H5001
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit, variant of H4651. Not a replaceable bulb — the entire unit is replaced. 12V.	H4652
ANSI standard (US & Canada). 5.75-inch round sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H5006
ANSI standard (US & Canada). 4x6-inch rectangular sealed beam unit. Not a replaceable bulb — the entire unit is replaced. 12V.	H4656

Other Locations

Additional Notes

The Mack MC uses three distinct headlamp configurations across the 1981-1991 model years: a 2-round-headlamp setup, a 4-rectangular-headlamp setup, and a 4-round-headlamp setup. Each configuration requires a different set of bulb sizes, and the correct fitment depends entirely on which headlamp arrangement the vehicle carries.
All bulb types specified for the Mack MC are sealed beam units conforming to ANSI standards recognized in both the United States and Canada. In a sealed beam design, the lens, reflector, and filament are fused into a single glass unit, meaning the entire assembly is replaced rather than an individual bulb.
The H6024 is a 7-inch round sealed beam unit operating at 12V. It serves as both the high beam and low beam bulb on the 2-round-headlamp configuration across all 1981-1991 model years, making it the only bulb type in these specifications that performs dual beam functions within a single fitment position.
The 4-round-headlamp configuration uses the H5001 for high beam and the H5006 for low beam throughout 1981-1991. The H5001 is a 4-inch square sealed beam unit, while the H5006 is a 5.75-inch round sealed beam unit, both rated at 12V.
The 4-rectangular-headlamp configuration uses 4x6-inch rectangular sealed beam units for both beam positions, but the specific variant differs by function and year. The H4651 covers the high beam role across all 1981-1991 model years, while the low beam position is filled by either the H4652 or H4656 depending on the year.
The H4652 and H4656 are both 4x6-inch rectangular sealed beam units and variants within the same physical format, but they are not interchangeable. The low beam position on the 4-rectangular-headlamp configuration uses the H4652 in 1981, 1987-1988, and 1991, and the H4656 in 1982-1986, 1989-1990.
Because the H4651, H4652, and H4656 share the same 4x6-inch rectangular form factor, substituting one for another may be physically possible but is not supported by these specifications. Each is assigned to a specific beam function and year, and cross-substitution falls outside the defined fitment data.
All six bulb types across the Mack MC specifications operate at 12V, which reflects the standard electrical system voltage used in commercial vehicle headlamp circuits of this type.