Abstract: A unique index mechanism for positioning an indexable machine tool member wherein a first toothed coupling is fixed to a machine tool base member, and a second relatively movable, toothed coupling having a uniformly spaced number of teeth unequal to the first uniformly spaced coupling teeth is located concentric to the first coupling on the machine tool base. The indexable machine tool member is carried by the second movable coupling, and a third toothed coupling with teeth disposed toward the first and second couplings is rotatably mounted to the machine tool in such fashion that the third coupling may be powered into and out of meshing engagement with the first and second couplings.The second coupling which carries the indexable machine tool member may be indexed to discrete angular increments corresponding to the angular difference in the tooth spacing of the respective first and second couplings.