Abstract: A precision workpiece positioner in the form of a rectangular parallelepiped has divided extensions projecting beyond one surface thereof for entry into the mouth of a locator slot in a machine tool table. Tapered expanders spread the divided extensions into positive engagement with the mouth of the slot. A screw engaged with the workpiece positioner draws a T-nut into tight locking engagement with the table which has a T-cross section. The positioner may be used in association with a workpiece clamp or plural positioners engaged in parallel table slots can align longer workpieces for machining.