An extruded insulator for a spark plug that is made in a manner that minimizes pores, relics and/or other defects in the insulator microstructure so that the overall dielectric strength or performance of the insulator is improved. The extruded insulator avoids many of the drawbacks associated with such defects, but also has a stepped internal bore for receiving a center electrode. In one embodiment, the extruded insulator is made with a method that uses a multi-phase extrusion process to extrude a ceramic paste around an elongated arbor and form an extruded section, and then removes the arbor from the extruded section to reveal a stepped internal bore.