How To Read a Feeler Gauge
Not quite sure about what’s the ‘right’ measuring fit for a feeler gauge? When taking readings with a feeler gauge, not only do you have to see the number on the metal plate but you also must be aware of what metric the device is measuring in. You also have to be vigilant to not measure with too little or too much friction.
What’s a Feeler Gauge?
A feeler gauge is a set of small, thin metal pieces that allow you to measure narrow gaps in either a hundredth of a millimeter or thousandths of an inch. If you’re wondering why anybody would need to measure such a small value, we’ll explain. Guitar manufacturers, the auto parts industry or anybody who can face uncertainty in perfecting small gaps for quality-assurance reasons requires this measurement.
How Do You Use a Feeler Gauge?
Guitar makers may use a feeler gauge to measure the distance between strings and the fretboard to perfect the working of the instrument. Feeler gauges can also be used to measure items such as piston rings, spark plug gaps, etc. Here’s how you use this device to measure narrow gaps:
Choose the Right Feeler Gauge
Feeler gauges usually come in a pile of 20-30 pieces — each plate has a different size. Choose a gauge that you think will be the right fit and unfold it from the pack from its pivot point. Try and fit it into the gap, and if you’re able to insert it with minimal force and little friction, you’ve found the right feeler gauge.
If the chosen gauge is slightly larger (has high friction) or smaller (no friction), try using the next best option. The goal is to find a gauge that fits into the gap with little friction. If you have a tapered feeler gauge, the thinner end will be the actual measurement.
You May Also Use Two Feeler Gauges Simultaneously
Sometimes, the gap won’t be so narrow and none of the feeler gauges will serve as the right fit. In this case, you can combine two feeler gauges and use them to find an accurate measurement.
Read the Measurement
Once you’ve found that perfect friction fit, you’re going to want to read the measurement on the feeler gauge. If the measurement has three numbers after a decimal point, the value is in thousandths of an inch. If there are two numbers after a decimal point, the value is in hundredths of a millimeter.
Oil Your Feeler Gauges After Using Them
Like any other tool, you must take proper care of your feeler gauges. The practice of oiling the gauges serves two purposes: it prevents them from getting stuck in the gap you’re measuring and keeps them protected from rust. Just drop a pea-sized amount of oil on the pile of feeler gauges and wipe them with a shop cloth. Make sure you open and close the pile enough times to ensure there’s a thin coat on every piece.
Keep This in Mind When Taking a Reading From a Feeler Gauge
The primary problem people encounter when taking a reading with a feeler gauge is that they’re unable to figure out whether they’re measuring in thousandths of an inch or hundredths of a millimeter. The second problem is that they’re unable to convert the value in inches to millimeters, or vice versa. Plus, if you had to use two feeler gauges simultaneously to measure one gap, you’ll have to add the two values to get the correct measurement — the units of both the gauges must be the same for you to find the right value (you can’t add a millimeter to an inch).
For example, if your feeler gauge says 0.040 — it is read as forty-thousandths of an inch. The same reading when converted to hundredths of millimeters would be 1.02.