- Machine Shop & Tool Repair Service, Chelmsford
- Machinery, Supplies & Equipment - Business Production Related, Chelmsford
- Machinery, Supplies & Equipment - Business Supplies Related, Chelmsford
- Machinery, Supplies & Equipment - Construction & Contractor Related, Chelmsford
- Magazine & Newspaper Stands, Chelmsford - Dealers & Distributors
- Mailing, Delivery & Courier Service, Chelmsford
- Malls & Shopping Centers, Chelmsford
- Management Consultants & Services, Chelmsford
- Manufacturing, Chelmsford
- Manufacturing Products, Chelmsford
- Marine Contractors & Designers, Chelmsford
- Masonry Contractors, Chelmsford - Stone Mason, Brick Mason - Install & Repair
- Masonry Materials & Supplies, Chelmsford
- Massage Therapists & Professional, Chelmsford
- Massage Therapy, Chelmsford
- Mechanical Floats, Chelmsford
- Membership Sports & Recreation Clubs, Chelmsford
- Men's Clothing Stores, Chelmsford - Clothes & Accessories
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- Metal Repair Service & Blacksmith, Chelmsford - Iron Works
- Mexican Restaurants, Chelmsford
- Mini & Self Storage, Chelmsford
- Mini Golf Courses, Chelmsford
- Mining Equipment & Supplies, Chelmsford
- Miscellaneous Agriculture, Chelmsford
- Miscellaneous Business Services, Chelmsford
- Miscellaneous Government, Chelmsford
- Miscellaneous Personal Services, Chelmsford
- Miscellaneous Professional, Chelmsford
- Motor Vehicle, Chelmsford
- Motor Vehicle Rental & Leasing, Chelmsford
- Moving Companies, Chelmsford
- Moving Truck Rental , Chelmsford
- Music, Chelmsford
- Musical Instruments Repair, Sales & Service, Chelmsford
- Musical Recording Services, Chelmsford
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