| 3117 | Macaroni and macaroni product manufacturing | |
| 3824 | Macaroni machinery manufacturing | |
| 3233 | Machine band, leather, manufacturing | |
| 3233 | Machine belt, leather, manufacturing | |
| 3212 | Machine embroidering | |
| 3813 | Machine guard, sheet metal, manufacturing | |
| 3829 | Machine gun manufacturing | |
| 3213 | Machine knitting | |
| 3829 | Machine part, machined, manufacturing | |
| 3420 | Machine ruling | |
| 3829 | Machine shop | |
| 3829 | Machine shop, repair work | |
| 3823 | Machine tool accessory manufacturing | |
| 3823 | Machine tool attachment manufacturing | |
| 3823 | Machine tool manufacturing | |
| 3823 | Machine tool rebuilding | |
| 3823 | Machine vise manufacturing | |
| 6100 | Machine, farm, wholesaling | |
| 3710 | Machined casting manufacturing, iron or steel | |
| 8102 | Machinery sales finance company | |
| 6100 | Machinery, electric, industrial, dealing | |
| 3720 | Machining non-ferrous metal castings | |
| 3811 | Machinists' precision tool manufacturing | |
| 3220 | Mackinaw, cloth, manufacturing | |
| 3220 | Mackinaw, short coat, cutting and sewing | |
| 3320 | Magazine back manufacturing | |
| 3829 | Magazine body, gun part, manufacturing | |
| 3420 | Magazine printing | |
| 3420 | Magazine publishing | |
| 9415 | Magician, own account | |
| 3699 | Magnesia cement manufacturing | |
| 3699 | Magnesia refractory manufacturing | |
| 3522 | Magnesia, medicinal, manufacturing | |
| 3699 | Magnesite grinding and treating, not at mine, pit or quarry | |
| 2901 | Magnesite mining or quarrying | |
| 3699 | Magnesite refractory manufacturing | |
| 3720 | Magnesium alloy in basic shape and form manufacturing | |
| 3720 | Magnesium bar cutting and finishing | |
| 3720 | Magnesium casting | |
| 3720 | Magnesium ingot manufacturing | |