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Hawaii first required its residents to register their motor vehicles and display license plates in 1922, while still an organized incorporated territory of the United States. It was admitted to the Union as the 50th state in August 1959.
Passenger plates 1922 to present
In 1956, the U.S. states and Canadian provinces came to an agreement with the Automobile Manufacturers Association that standardized the size for license plates for vehicles, except those for motorcycles, at six inches in height by twelve inches in width, with standardized mounting holes.
From 1969, the upper right screw hole has been round. The other screw holes are horizontal slots.
References
Vehicle registration plates of Hawaii Wikipedia(Text) CC BY-SA