In this Tool Tutorial, you’ll learn:

• What a feeler gauge is
• Its common uses 
• How to use one to measure a spark plug gap

What is a “Feeler Gauge?”

The tool contains a series of small blades inside a metal container that can be bought individually or as a kit.

However, these blades aren’t for cutting – they’re for measuring. 

Each blade has a stamp of its thickness on the side. For example, this blade has a thickness of 0.40 mm (or approximately 0,02 inches):

Uses of a Feeler Gauge

• Measuring spark plug gaps
• Measuring valve play in an overhead camshaft engine

Using this tool is fairly simple – on the tool difficulty scale, it ranks at a difficulty rating of 1 (very easy to use).

If you can use a rule or a tape measure, you can learn to use this tool within less than a minute.

How to use a feeler gauge – step-by-step

1. Bring out the object whose gap you want to measure (in my case, I’ll use a spark plug)
2. Fold out one of the blades and stick it into the gap you want to measure:

The blade is supposed to go into the slot with little to no wiggle room.

If you’ve got too much wiggle room, you need to choose a thicker blade.

If you can’t get the blade through the gap, you need a thinner blade.

Look at the specs on the side of the blade and note the measurement. In the image above, the blade had a with of 0.50mm – therefore, the spark plug gap is 0.50mm wide.

And there you go – you now have your measurement!