Be aware that the description of this item is incorrect, with the exception of the manufacturer's description line.  This part is for the older "classic" series of Drill Doctors, NOT for the newer version that Amazon now sells.  Only the models without the trailing X in the model number can use this.  All of the lines above that say it is for ...500X, 750X are incorrect.  It is the wrong diameter, as the newer wheels are smaller.