I have a Bosch ROS20VS ROS grinder and this adapter does not fit my grinder in any way. The outside diameter of the grinder shaft is 1.125 inches. The entry at the threaded end of the adapter is 1.375" or 1/8" wider than the shank. The other end is even bigger. Looking at other reviews of this adapter, all I can think of is that there are supposed to be several grinders of different sizes under the model number ROS20VS.