Feeler gauges are a common machinists tool used to measure small distances between objects. A traditional set of feeler gauges consists of 12 to 36 different strips of sheet metal that vary in thickness from .002" to .040" thick. The metal strips are usually pinned together on one end allowing them to be portable and easy to keep track of. Guitar repair feeler gauges are no different than regular machinist feeler gauges. Guitar gauges just have specific uses that are unique to the guitar.
Feeler gauges are used to measure very small distances. For instance, you can place a feeler gauge in between your guitar string and the fret to see how high the fret is above the fret. Feeler gauges can be used to measure many differ parts on your guitar. One use for a feeler gauge is when you are making a guitar nut. Once you have the guitar nut glued in place, you can place the appropriate feeler gauge against the fretboard along side the nut and use it to measure the desired height of the nut. After you mark it with a pencil, you can file the nut blank down to the desired height. Feeler gauges can also be used to measure the action of your guitar strings. Simply, hold down the sixth string at the neck joint and place a feeler gauge under the sixth or seventh fret. This will tell you how much relief or back bow your neck has in it.
Feeler gauges can be used to measure many other guitar parts, but these two are the most common. Without a doubt, you need to add a set of feeler gauges to your growing list of guitar repair measuring tools. Feeler gauges allow you to be accurate in your measurements and your guitar setups. The best thing about feeler gauges is that they are inexpensive. Go pick up a set today; your setups will be more accurate from now on! If you would like more information about how to set up a guitar, please see my how to set up a guitar article.