A milling cutter for cutting a workpiece in both right and left-handed rotary directions is provided that comprises a rotatable cutter body having at least one pair of right and left-handed insert seats disposed on its periphery, an indexable wedge for each pair of right and left-handed insert seats, and a mounting screw for each of the wedges for securing the wedges in a clamping position with respect to a right or left-handed insert seat. Each of the wedges may be used to secure an insert in the right or left-handed seat of its respective seat pair by loosening or removing the mounting screw, and turning the wedge 180.degree.. Each wedge includes a front end for wedgingly engaging an insert in either the right or left-handed seat, and a back end for wedgingly engaging an opposite surface of the unused insert seat in order to more securely clamp the insert in place. The back end of each wedge includes an offset portion that is receivable in and semi-complementary in shape to the unused insert seat for still more stability.