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M # Symbol

Current M-Number Listing

How to Apply for an M#/Symbol

Submit a M # Symbol Approval requests using the PHMSA Portal

Applicants also have the option of submitting request via email to, or mailed to [Department of Transportation, East Building, PHH-33, 1200 New Jersey Avenue SE, Washington, DC 20590]

NOTE: Please attach an individual request, when applying online

The M#/Symbol registration request should contain the following:

  • Request Letter as described in 49 CFR 107.705
  • The Request Letter must contain detail information for the purpose of the M#/Symbol and the item that is being mark with the M#.
  • Provide the name, facility and mailing address, email (optional), and the telephone number of the person on whose behalf the registration or application is made and, if different from the person filing.
  • If the company seeking registration is an international location, they must provide an U.S. Agent name, company, and contact information attached to their request. 

Requests for confidential treatment must be marked in accordance with 49 CFR 105.30.

Manufacturers Symbols

A symbol or "M Number" is issued to a company as a means of identification. Under certain regulations, the M number must be used solely as the identifier on a package, for example DOT 39 nonrefillable cylinders, 49 CFR 178.65(i)(2). However, other regulations allow the manufacturer to use either the symbol or their name and address as specified in 49 CFR 178.3(a)(2).