then this accessory is your solution. I recently bought a used 4210 mount and had to buy a new mount anyway. I chose to buy it from Porter-Cable to use the original equipment, but they only supply a 1/2" shank. one piece. The problem is that my only 1/2" end mill is what I'm using in my router chart, and the end mill I'm going to use for this only has a 1/4" shank. So I researched and found this. Received, tried, works as it should, no problems.