| 1. Resistor | None--No Resistor | R--Mil-Spec. Resistor-Erosion protection |
| 2. Barrel Style | None -- Unshielded | E -- Shielded 5/8"-24 Thread |
| H -- Shielded 3/4"-20 Thread (All Weather Plug) |
| 3. Mounting Thread -- Reach -- Hex Size | B-18mm 13/16" / 2.06cm 7/8" / 2.22cm | M--18mm 1/2"/1.27cm 7/8"/2.22cm |
| L-14mm 1/2"/1.27cm 13/16/2.06cm | U18mm 1-1/8"/2.85cm 13/16/2.06cm |
| J -- 14mm 3/8"/0.95cm 13/16/2.06cm |
| 4. Heat Rating Position | Low number--cold | High number--hot |
| 5. Electrode Design | None-Conventional single | E -- Two prong massive N -- 4 prong massive |
| W -- Fine wire (Iridium) | B --2 prong massive, Tangent to Center |
| P--Fine wire (Platinum) |