How to Read Spark Plug Part Numbers

A spark plug part number is a spec sheet in disguise. Once you know the pattern, you can read thread size, reach, heat range and tip type straight off the box.

NGK

NGK codes start with a letter for thread/hex, then a construction letter, then a heat-range number (higher = colder), then reach and tip letters. Example: in BKR5E, the 5 is the heat range and E indicates reach.

Denso

Denso uses a letter prefix for thread, then a heat-range number — but Denso's scale runs the opposite direction to NGK (higher = hotter), which is a classic cross-reference trap.

Champion, Bosch, Autolite, ACDelco

Each has its own scheme; Autolite and ACDelco lean on numeric part numbers where the pattern encodes application and heat range rather than being human-readable at a glance.

The catch with heat range

Because the scales differ — and sometimes reverse — comparing heat-range numbers across brands by eye is unreliable. That's the whole reason to use a tool that normalizes them.

Next

Understand the metals behind the tiers in the copper vs platinum vs iridium guide, or find equivalents with the cross-reference guide.