Just one note about the Robust collets...they are fairly dust sensitive.At least, that is the only excuse I can find for a failure of one. I had one jam and it was not cross threaded - it was tightened with only light hand pressure only...and it could not be loosened. Not even after destroying it with a pipe wrench and bench vice. So, the only thing I can say is that I believe that tight tolerances are good thing most of the time....but not all of the time. I was surprised to say the least.