How to choose a water pump motor rotor

Water pumps usually have a brushless motor and the rotor is selected based on the diameter of the wide magnetic part and the mounting seats. The diameters are measured with high accuracy, the length with an accuracy of 1-2 mm. length_2 is the distance between the bearings. length_3 is the length of the magnetic coating. length_4 is the length of the shaft from the blank.