It fits a Foredom threaded handpiece perfectly, as well as a Dremel with the threaded nose (they screw into the crossbar). It requires assembly but it's easy to figure out: remove the two little screws with the included hex wrench, insert them through the base plate into the countersunk recesses, and into the threaded vertical supports. You can add a dot of blue Loctite to each screw if you like. When you assemble it, pay attention to the little air tube sticking out of the crossbar; this is where you can connect an air hose to blow away the chips/dust and keep the work clear of debris. Most techs have the tube pointing to the 'closed' side of the base plate so the hose stays out of the way as they work, looking through the 'open' side of the base plate. To use it, screw the large thumbwheels all the way down. Insert the rotary tool with cutter into the crossbar and snug it in place. Adjust the top thumbscrews to set the depth of cut, and then rotate each large thumbwheel upward to lock the crossbar in place. You're ready to work.

Nice attachment, worked just like I needed it too.