- Machinery And Equipment Manufacturers, Port Washington
- Machinery Custom Design Manufacturers, Port Washington
- Machinery, Supplies & Equipment - Business Supplies Related, Port Washington
- Machinery, Supplies & Equipment - Construction & Contractor Related, Port Washington
- Maintenance, Cleaning & Sanitation, Port Washington
- Management Consultants & Services, Port Washington
- Manicurists & Pedicurists, Port Washington
- Manufacturers Agents & Representatives, Port Washington
- Manufacturers Representative, Port Washington - Reps, Independent Sales Representative, Sales Agent, etc
- Manufacturing, Port Washington
- Manufacturing Products, Port Washington
- Marinas & Marina Services, Port Washington
- Marine Supplies & Equipment, Port Washington - Boat Supplies
- Marriage & Family Counselors, Port Washington
- Masonry Materials & Supplies, Port Washington
- Meat Market, Wholesale & Products, Port Washington
- Membership Sports & Recreation Clubs, Port Washington
- Men's Clothing Stores, Port Washington - Clothes & Accessories
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- Mental Health Specialists, Port Washington - Psychologist, Psychiatrist, Psychotherapist, etc
- Metal Stampings Manufacturers, Port Washington
- Mildew Removal & Control, Port Washington - Mold Removal
- Mini Golf Courses, Port Washington
- Miscellaneous Agriculture, Port Washington
- Miscellaneous Government, Port Washington
- Miscellaneous Manufacturing, Port Washington
- Miscellaneous Metal Work Manufacturers, Port Washington
- Miscellaneous Professional, Port Washington
- Mobile Home Parks & Communities , Port Washington
- Mortgage Bankers & Correspondents, Port Washington
- Motor Vehicle, Port Washington
- Motor Vehicle Rental & Leasing, Port Washington
- Motorcycle Parts, Accessories & Dealers, Port Washington
- Moving Companies, Port Washington
- Moving Truck Rental , Port Washington
- Music, Port Washington
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