Mortiser chisels cut better if you use a spacer to create a gap between the chisel and the internal drill bit. A dime’s thickness is about the right amount of gap, but for me it would often drop off as I installed the chisel and tightened things up. Instead of using a dime, I cut a piece of thin kitchen magnet to “stick” between the collar and chisel for a spacer. After use, I just stick the magnet to the mortiser until next time. No more dropping those dimes!