Note that your belt-buckle's form is a much longer rectangle than is usually seen. That version is known as a College/School buckle. See page 523 in the book "American Military Belt Plates" for an example of that type (which says Georgia instead of NMMI like yours) and historical info about them. According to that book, they date from circa 1900 to 1925.
The book says:
"Popular style of early 20th Century school plate marketed by several firms. The 1916 North & Judd catalog (New Britain, Conn.) listed these as 'College buckles.' They offered to make up new designs with different school names at no extra cost provided a gross [144] or more were ordered. Thomas Parry & Sons advertised these as 'College Belt Buckles' in the same period."