How To Use A Feeler Gauge

Precise measurements and knowing how to use a feeler gauge are not always commonplace in the automotive world. After all, how many times do you need to measure brake pads by the 0.001”.

While feeler gauges and other precision measuring tools are not used often, they are vital when needed. Measuring cylinder head flatness, piston ring gaps, and thrust clearances require the feeler gauge. Knowing how to use a feeler gauge is just as important as having the best set of the gauges that suit your needs. 

So, if you have ever been left scratching your head looking at those small numbers on those small blades. Fear not, we are going to demystify the process and turn you into a feeler gauge expert. 

What Is A Feeler Gauge?

A feeler gauge is a precision measuring tool that you will find in the toolbox of mechanics, machinists, and do-it-yourselfers. The tool itself consists of thin metal strips, each having a specific thickness. 

The metal strips are referred to as blades. Each blade ranges in thickness from paper thin up to 0.050” or larger depending on the set. While there are many different blades, each fits nicely into the compact case for easy storage in your toolbox. 

A feeler gauge’s main purpose is to measure the clearance or gap between surfaces. This ensures that perfect alignment and precision fit. 

Using A Feeler Gauge

When the online service manual tells you to measure something to 0.001” it can be scary. We have created a simple step by step procedure below to complete the job with confidence.

Clean the surfaces

The first and most important step to get accurate measurements is to make sure you have a surface that is clean. Make sure all debris and oils are removed from the surface before measuring. This will also allow the blade to fit tighter, resulting in a more accurate measurement. 

Select the right sized blade

Your feeler gauge set will have multiple different sized blades. Determine the size of the blade that you will use by referring to the specified measurement in the manual. 

For example, if you are measuring a clearance that is 0.005”, start with a feeler gauge blade that is sized 0.003”.

Insert the blade

Use your thumb and index finger to hold the feeler gauge. You will position the feeler gauge in a way that allows you to slide the feeler gauge blade into the gap you are measuring. Sometimes this means that it will be parallel with your index finger or perpendicular.

Making The Measurement

Now that the feeler gauge is ready, it is time to take the measurement. 

Feel for resistance

This is the most important step when it comes to getting an accurate measurement. You need to slide the feeler gauge gently and feel the resistance that is present when it is moving. 

You are looking for a very slight amount of resistance to movement.

Finding the right fit

If you find there is no resistance when moving the blade, it indicates that the gap is larger than the feeler gauge blade. You will need to move up in size and measure again. 

If you cannot move the feeler gauge blade, it indicates that the gap is smaller than the feeler gauge. You will need to use a feeler gauge blade that is smaller in size and measure again. 

Check the measurement

Now that you have the feeler gauge blade that has slight resistance it is time to read those small numbers. The number that you read on the blade is the measurement of the clearance between the two objects. 

So, if for example the feeler gauge reads 0.005”. This means that the clearance between the two objects you are measuring is 0.005”

Repeat and double check your measurement

To make sure that your measurement is correct, double check your measurement. If the readings are not consistent, make sure that the two surfaces are clean and you are feeling for slight resistance. 

Tips and Tricks

Becoming a master in the use of a feeler gauge requires practice. There is nothing that replaces the feel that you need to identify that “slight” resistance that is so important. With the right tricks you will be a pro in no time. 

Keep the tool parallel when measuring

This is very important and changes with every measurement that you take. It is recommended that you keep the tool perpendicular to what you are measuring. 

However, in the real world this is very hard to do. You may need to hold the blade of the feeler gauge perpendicular or even at an angle. Whatever direction you need to hold the blade it is very important that you keep the tool parallel when sliding it.  

Don’t force the blade

Blades are never meant to be forced. If you force the blade it can be easily damaged or bent. If the blade doesn’t fit what you are trying to measure, use a smaller blade and measure again. 

Label your feeler gauge set

While knowing how to use a feeler gauge set is important. It is absolutely vital that you can find the tool to use it.

Mark your set by engraving your initials or by giving it a shot of spray paint with a color that is unique to your tools. 

Oil before storage

Feeler gauges are not used very often, this can lead to serious problems when the tool is stored. The feeler gauge blades are made of bare steel because they are precise measuring tools. 

This means they have no protection from rust. Make sure that when you are done using your feeler gauges you coat them in a light machine oil. After coating them, store them in a ziploc bag to protect them even more. 

Doing this one simple step will make sure that your feeler gauge set is ready to use the next time you find yourself measuring cylinder head warpage. 

Conclusion

Well, we have done it. We have given away all the secrets of how to use a even the best feeler gauge sets correctly. As you can see there is a little bit of knowledge and feel needed to use this precision measuring device correctly. 

With a little bit of experiencing you will be measuring clearances to the thousandths of an inch with the accuracy of an old pro. Even changing spark plugs and gapping them will be a breeze.

FAQs (Frequently Asked Questions)