A spark plug (10) includes an intermediate connecting pin (54) disposed in the central passage (28) of an the insulator body (12). The connecting pin (54) seats in an intermediate taper section (72) within the central passage (28), which is generally frustoconical and establishes a transition between a first larger diameter of the central passage (28) and a second smaller diameter. The intermediate tapered section (72) is located longitudinally above a filleted transition (26) feature of the insulator body (12) exterior. A pin head (53) of the connecting pin (54) has a complementary tapered under-cut and seats against the intermediate tapered section (72) to provide self-centering of the connecting pin (54) without trapping gas during the assembly process. The intermediate taper section (72) also provides an increase in insulator wall thickness which improves dielectric capacity and structural integrity of the insulator (12).