The Part# 1110ER is a 1 inch diameter arbor that has a 3/8" diameter Shank to fit in a 3/8 ER16 collet. It has a 1/2 inch lip on the end. The lip is what registers the slitting saw so that it runs concentric.
Note: This does not fit the ¾-16 head stock, use Taig-1110 instead.