By measuring the size of a car horn calculate effective vibration radius. That is according to the outer edge of the cone is not pressed into a fixed diameter apron count, it is customary for the speaker’s caliber in inches. Most people use more metric ruler, measure the cone after how many centimeters in diameter, divided by 2.54 (2.54 cm equals one inch), is an inch. 4-inch speaker: the screw holes on the angular distance is 11.5 cm, 8 cm adjacent pitch, speaker diameter is 10 cm; 5-inch speaker: the screw holes on the angular distance is 13.5 cm, 9.5 cm adjacent pitch, diameter 13 cm; 6.5-inch speaker: the screw holes on the angular distance is 15.5 cm, 11 cm adjacent pitch, diameter 16.5 cm; 4X6 inch screw holes adjacent distance is 12.3 cm and 7.3 cm; 6X9 inch screw holes adjacent distances are 16.5 cm and 11 cm.