The measuring horn (speaker, jargon "unit") is sized according to the effective vibration radius. That is, according to the diameter of the fixed apron that is not pressed into the outer edge of the paper cone, it is customary to use the inch of the horn.
The ruler used by most people is metric. How many centimeters after measuring the diameter of the cone is divided by 2.54 (2.54 cm is equal to one inch), which is inch.
4-inch speaker: the diagonal distance of the screw hole is 11.5 cm, the adjacent hole spacing is 8 cm, and the horn diameter is 10 cm;
5-inch speaker: the diagonal distance of the screw hole is 13.5 cm, the adjacent hole is 9.5 cm away, and the caliber is 13 cm;
6.5-inch speaker: the diagonal distance of the screw hole is 15.5 cm, the adjacent hole is 11 cm apart, and the diameter is 16.5 cm.
4X6 inch adjacent screw hole distance is 12.3 cm and 7.3 cm;
The 6X9 inch adjacent screw hole distances are 16.5 cm and 11 cm, respectively.