What Is The Thread Size Of A Spark Plug?

What Is The Thread Size Of A Spark Plug

Nothing can beat the satisfaction of being able to fix your car by yourself. Besides, how hard is it to replace a vehicle’s spark plug? You could save yourself some money and brag to your friends about it! If you’re starting out, you might ask yourself what the thread size of a spark plug is and which type you need.

In this article, we have you covered with all you should know about spark plug threads, how they are measured, and a handy spark plug thread size chart at the end.

How to Measure Spark Plug Thread Size

A spark plug thread size consists of three parameters; reach, diameter and pitch.

  • The thread reach of a spark plug is the distance between the thread’s beginning, i.e., the plug’s base and the end of its thread, excluding the ground electrode and the gasket (for gasket plugs). 
  • Thread diameter is the distance across the plug’s thread. 
  • The pitch is the distance between two consecutive grooves of a thread on the plug. Thread diameter and reach are often written together. For example, the first number indicates the diameter for M10 x 1.0mm plugs, and the second number indicates pitch.

In brief, the thread size of a spark plug indicates the size of the thread that will be screwed into a cylinder head. Although there is no standard size for spark plugs, 16mm is the most common spark plug thread size. Below is a spark plug thread size chart that you can use for future references.

spark plug thread size chart (Source)


Are spark plug threads universal?

No, spark plug threads are not universal, and you should not use other sizes than the factory recommended thread size.

Can I use any spark plug?

As long as you use spark plugs with the correct dimensions and heat range, you can use spark plugs from different brands interchangeably without any problems.

What happens if I use the wrong spark plug?

In case you have installed the wrong spark plug, it will cause constant rattling and knocking noises from the engine. If the vehicle feels jerky and disjointed, the chances are that your spark plugs are not working properly. It also risks damaging the engine as it would pre-ignite and misfire, putting stress on the engine.

Can I use WD40 on spark plugs?

Yes, using WD-40 on your spark plugs helps repel water and protects them from corrosion as moisture is prevented.


Working on your own car is an underrated job as it leaves you satisfied and saves a considerable amount of money in the long run. However, as spark plugs are one of the most crucial components of an engine, they require frequent maintenance. If you were wondering about what is the thread size of a spark plug, we hope to have helped you gain insights from this article.

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