Perfect for most 3018 CNC Routers on the market, including Genmitsu 3018-PRO, 3018-PROVer, 3018-PROVer Mach3, 3018-MX3, 1810-PRO. The diameter of the motor is 44mm. (Note: The stock spindle holder of the 3018 CNC machine could hold the spindle which diameter is between 42mm and 44mm )