I think the main problem with the concept on this mill is that the taper for an ER16 is so small that there is not enough surface area to generate enough friction to hold a tool securely, unless it is in there tighter than you can get it with belleville washers and still get it out easily. Even the ER16 nut is made to pop the collet out, as it has to really be wedged in there for a 3/8" end mill. I can see something working for 1/8 shank tools, though, for people who use those, exclusively.