I needed a small chuck to use with really small drills. All the nicely made 3 jaws I had would not close up on small drills. I took the chuck out of an old Makita and turned the shaft to 3/8". I have not even tried to measure run out as it works awesome in the smallest work. I regularly use #50-60 drill bits and sometimes even smaller. I use it with a collet in the mini mill but I have also mounted in a drill press, works great.