Mack CM Headlight Bulb Size

Mack CM headlight bulb sizes include H6024, H4651, and H5001 for high beam applications, along with H6024, H4656, and H5006 for low beam configurations, with each bulb size corresponding to specific lighting functions. The replacement chart covers 1988 through 1991 production years and details bulb size specifications for each model year.

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
1988-1991	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)
	H4656 (With 4 Rectangular Headlamps)
	H5006 (With 4 Round Headlamps)
1988-1990	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. Not a replaceable bulb — the entire unit is replaced. 12V.	H4656
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, variant of H4651. Not a replaceable bulb — the entire unit is replaced. 12V.	H4652

Other Locations

Additional Notes

The Mack CM covers model years 1988-1991 in these specifications, and across all four years the headlamp system varies by configuration: two-round, four-round, or four-rectangular headlamp arrangements, each requiring a distinct bulb type for both high and low beam positions.
All six bulb types referenced in these specifications, H6024, H4651, H4656, H5001, H5006, and H4652, are sealed beam units operating at 12V and conforming to ANSI standards recognized in both the United States and Canada. In a sealed beam design, the lens, reflector, and filament form a single fused unit, so the entire assembly is replaced rather than an internal bulb.
The H6024 is a 7-inch round sealed beam unit and serves as both the high beam and low beam bulb on CM models equipped with the two-round headlamp configuration across all listed years. A single part number covering both functions in a two-lamp system is typical of designs where each sealed beam unit contains dual filaments.
The four-rectangular headlamp configuration uses different part numbers for high and low beam positions. The H4651 handles the high beam role across 1988-1991, while the low beam role is filled by the H4656 in 1991 and by the H4652 in 1988-1990. The H4652 is described as a variant of the H4651, and both share the 4x6-inch rectangular sealed beam format.
The substitution of H4656 for H4652 in the low beam position of the four-rectangular configuration in 1991 represents a fitment distinction that makes these two part numbers non-interchangeable across all listed years despite their shared physical format.
The four-round headlamp configuration uses the H5001, a 4-inch square sealed beam unit, for the high beam position and the H5006, a 5.75-inch round sealed beam unit, for the low beam position. The physical size difference between these two units means they are not interchangeable between positions.
The H5001 and H5006 pairing for the four-round configuration remains consistent across all four model years in the specifications, as does the H4651 high beam assignment for the four-rectangular configuration, indicating stable fitment requirements within those headlamp types throughout the 1988-1991 range.
Because the headlamp system on the Mack CM varies by physical configuration rather than by model year alone, the correct replacement unit depends on whether the vehicle carries two round, four round, or four rectangular headlamps, and on whether the position being serviced is high beam or low beam.