The NEMA provides all sketchs in inches but only the External Construction Sizes, all this NEMA sizes are intended to ilustrate and help in the mounting works.
Unfortunatelly the NEMA Sketchs don´t provide the core sizes.
The 182T core lengt depends of manufacturer desing and is not a constant, But this size could change from 2.75 up to 4 INCHES.You could find differences due to the motor´s Power output, a 1.5 HP motor have more core than 1 HP.
No standard regulates the core length of motors. Different designs can be "packed" into a 182T frame size. The core length is defined by each manufacturer design.
