Mack DMM Headlight Bulb Size

Additional Notes

• The Mack DMM uses sealed beam headlamp units across all three headlamp configurations for the 1981-1997 model years. All bulb types specified, including the H6024, H4651, H4652, H4656, H5001, and H5006, are ANSI-standard sealed beam units rated at 12V, meaning the entire lens-and-filament assembly is replaced as a single unit rather than a separate bulb being swapped within a housing.
• The H6024 is a 7-inch round sealed beam unit and serves as both the high beam and low beam source on Mack DMM vehicles fitted with the 2-round-headlamp configuration across the full 1981-1997 span. Its use in both functions within that configuration is a characteristic of certain sealed beam designs where a single unit handles the full lighting range.
• On Mack DMM vehicles equipped with 4 round headlamps, the high beam position uses the H5001, a 4-inch square sealed beam unit, while the low beam position uses the H5006, a 5.75-inch round sealed beam unit. These two units are not interchangeable with each other due to their differing physical forms and beam functions.
• The 4-rectangular-headlamp configuration on the Mack DMM separates high and low beam duties between distinct sealed beam types. The H4651 handles high beam output, while the low beam position is filled by either the H4652 or H4656 depending on the model year, both of which are 4x6-inch rectangular sealed beam units.
• The H4652 is specified as a variant of the H4651 within the 4x6-inch rectangular sealed beam family. Despite their physical similarity, the H4651 and H4652 are assigned to different beam positions and are not listed as interchangeable within these specifications.
• Within the 4-rectangular-headlamp configuration, the low beam position alternates between the H4652 and H4656 across different model years. Both are 4x6-inch rectangular sealed beam units, but they carry distinct ANSI designations and are listed separately by year rather than as substitutes for one another.
• All six sealed beam types specified for the Mack DMM conform to ANSI standards recognized in both the United States and Canada, placing them within a standardized sizing and performance framework common to North American commercial vehicle lighting of that era.
• Because every headlamp type across all three configurations is a sealed beam unit, fitment is governed by the physical housing format of the vehicle rather than a bulb socket type. The 2-round, 4-round, and 4-rectangular configurations each require their own distinct set of sealed beam units, and units from one configuration are not compatible with the housings of another.