| 3320 | Magnifying glasses (except vision correcting type), manufacturing | |
| 3320 | Magnifying glasses, manufacturing | |
| 3320 | Magnifying instruments, optical, manufacturing | |
| 1310 | Magnoferrite mining | |
| 7493 | Maid cleaning services | |
| 7491 | Maid registries | |
| 1810 | Maids' uniforms, cut and sewn from purchased fabric | |
| 7499 | Mail box centres, private | |
| 4530 | Mail boxes erection (residential-outdoor) | |
| 2899 | Mail boxes, light gauge metal, manufacturing | |
| 6023 | Mail carriers, bulk, contract, local | |
| 2811 | Mail chutes, sheet metal, manufacturing | |
| 6412 | Mail delivery, private (except air) | |
| 3000 | Mail handling machinery, Post Office type, manufacturing | |
| 5150 | Mail handling machines, wholesale | |
| 5251 | Mail order houses | |
| 5251 | Mail order offices of department stores | |
| 3610 | Mail pouch racks (except wood), manufacturing | |
| 3610 | Mail pouch racks, metal, manufacturing | |
| 6412 | Mail service, contract | |
| 6411 | Mail service, government | |
| 6210 | Mail transportation, air, scheduled | |
| 2102 | Mailing cases and tubes, paper fibre (i.e., fibre body, ends of any material), made from purchased paperboard | |
| 7499 | Mailing list compilers | |
| 7499 | Mailing list publishers | |
| 7499 | Mailing list, compiling service | |
| 5150 | Mailing machines, wholesale | |
| 3610 | Mailing racks, postal service (except wood), manufacturing | |
| 3610 | Mailing racks, postal service, metal, manufacturing | |
| 3000 | Mainframe computers, manufacturing | |
| 4520 | Mains, gas, construction | |
| 7493 | Maintenance and cleaning of shopping malls | |
| 7250 | Maintenance and repair of computers and related equipment | |
| 7493 | Maintenance of buildings and dwellings, janitorial | |
| 6303 | Maintenance of piers, docks, wharves | |
| 0140 | Maintenance of plants and shrubs in buildings | |
| 0140 | Maintenance of rights-of-way (i.e., controlling vegetation) | |
| 4520 | Maintenance of rights-of-way and structures, railway | |
| 2930 | Major appliances, electric and non-electric, manufacturing | |
| 9241 | Major league baseball club | |