so it holds the bit.  My last collet got scratched or bent or something.  It wouldn't grip correctly and the bit would work its way up and down while cutting.  Aside from a bad cut it was dangerous.  This one does what the other used to do.  It holds the bit like it is supposed to.  Plus I like the retaining ring to hold the nut to the collet.  Makes it easier to change the collet size all at once, no finding parts and such.