fractional horsepower motors use 2-digit frame designations, integral use 3-digit frames.
First 2 digits always shaft height in inches times 16 (small machines) or times 4 (larger machines).
For example, frame 48 has 3” shaft height.
445 has shaft height of 11”.
The 5 at the end of 445 can be used to determine length by table lookup. Many more dimensions are defined which help to ensure mechanical interchangeability of motors.