Free tool
NGK Spark Plug Decoder & Plug Reading Guide
Decode an NGK small-engine spark plug number such as BPMR7A or CMR6H, and diagnose your chainsaw from the color of the plug tip.
Try:
Read your plug
Tap the tip that looks most like yours.
Spark plugs and saw parts
Reading an NGK part number
NGK numbers are a code. The first letter is the thread diameter, the next letters describe the construction, the number is the heat range and the trailing letters cover reach and special features. On NGK plugs a lower heat number means a hotter plug. Two plugs that only differ by a letter can still be different lengths, so when replacing a plug, use the exact number listed in your saw’s operator’s manual.
What a plug tells you
Pull the plug after a run and look at the insulator tip. Light tan to gray means the engine is running right. Black and sooty points to a rich mixture or a clogged air filter, wet and oily points to too much oil or a flooded engine, and white or blistered can mean a lean, hot-running engine that needs attention before it seizes.
Common questions
What does the R mean in BPMR7A?
R means the plug has a built-in resistor, which suppresses radio-frequency interference.
How often should I replace a chainsaw spark plug?
Many manufacturers suggest checking the plug every season or every 100 hours or so, and replacing it when the electrode is worn, the insulator is cracked, or the saw is hard to start.