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Sometimes the gap between objects or parts can be bigger or smaller than required and this can cause problems. This applies especially to systems or subsystems that need precision measurement between them or their parts. A perfect example is a car engine. It has several parts that seem flush or in contact with each other while in reality, most have very small gaps between them. If these gaps are ignored during an engine rebuild exercise, they can cause poor engine performance. For instance, an incorrect engine valve clearance can cause the engine to run rough. This is why you need a precision tool such as a feeler gauge for valve clearance. Feeler gages are also useful for measuring the flatness of engine surfaces such as the cylinder head and setting up a guitar’s Action among other uses.
What is a Feeler Gauge?
A feeler gauge is a precision-measurement tool for measuring the thickness of very narrow gaps and the flatness of surfaces. It consists of either a stack of metal sheets or wire strips of known thickness or gauge. There are various types of feeler gauges but the most common types are the steel feeler gauges, brass feeler gauges, and wire feeler gauge.
Types of Feeler Gauges
1. Steel Thickness Gauge
Set As the name goes, steel feeler gauges are made of steel. However, for increased strength and flexibility, carbon is added to make tempered carbon steel or stainless steel. Some steel feeler blade tools are made of alloys of manganese. Comparatively, the stainless steel feeler gauges are superior to other varieties of steel gauges because they do not rust. The others rust very quickly in humid shop conditions if they are not oiled and sealed properly.
2. Brass Feeler Gauge Set
The brass thickness gauge tool has brass feeler blades. This type of feeler gauge is non-magnetic or non-ferrous if you like. This property makes it suitable for applications where there is a magnetic field. Unlike the magnetic steel feeler blades, the brass leaflets do not stick to magnets thus allowing you to work effectively around magnets or electromagnets. You can use a brass thickness gauge to set the air gap between the reluctor sensor and trigger teeth when configuring the engine cam. Other applications of brass feeler gauge include: setting the air gap in electronic ignition, harmonica repair, harp repair, and setting the air gap on a distributor. You can also use it to perform the tasks of the ordinary feeler gauge such as engine repair and spark plug gapping. One advantage of the brass feeler set over the steel thickness set is that it does not rust. So you do not need to drench it in oil as you would do with the latter.
3. Round Wire Feeler Gauge
A wire-type feeler gauge is fondly known as a gapping tool. It is made of wire loops of calibrated sizes. Although it can be used like other feeler gages, this tool is mostly used to gap spark plugs. Its small in size and has a limited number of gauge sizes which make it unsuitable for many applications. A round feeler gauge expands the gap of a spark plug very easily and effectively.
Feeler Gauges Comparison Table
|Proto J000TL 25 Blade Long Feeler Gauge Set||Starrett 66B Thickness Gage Set With Straight Leaves||Precision Feeler Gauges||ABN Universal Standard SAE and Metric Offset Valve Feeler Gauge||Hotop Steel Feeler Gauge Dual Marked Metric and Imperial Gap Measuring To|
|Buy from Amazon||Buy from Amazon||Buy from Amazon||Buy from Amazon||Buy from Amazon|
|Number of Leaves/blades||25 blades||31 leaflets||32 Leaves||16 blades||32 blades|
|Design||Straight set||Straight set||Straight set||Angled set||Straight set|
|Range||.0015" - 0.040"||0.0015" - 0.035"||0.0015" - 0.035"||0.05" - 0.019"||0.0015" - 0.035"|
|Buy from Amazon||Buy from Amazon||Buy from Amazon||Buy from Amazon||Buy from Amazon|
Best Thickness Gauge Tools Full Reviews
Proto Feeler Gauge Review (25 blade)
Proto feeler gauge set (J000TL) has 25 blades bound within a steel blade holder. Each blade is 12 inches long and 1/2 inches wide with the thickness size laser-etched on one side in both empirical and metric units. However, the main scale is empirical.
This super long feeler gauge is most suitable for measuring gaps in very tight spaces. Furthermore, when the tips of the long feeler leafs start to wear down, you can just cut the end off and still remain with adequate length to allow you to carry on with measuring. This makes proto the best feeler gauge on the market.
- Feeler gauges are long enough to access deep places
- When the tip wears down, you can cut the end off and be left with reasonable length
- Amercian made
- Does not ship with a case
Although a little bit pricey, the J000TL proto feeler gauge is a great precision measurement tool, especially for long reach measuring. It is ideal for applications such as measuring the flange gap during pipe stress, valve adjustment on horizontal engines (such as the boxer engines), and blower lobe clearance among other applications.
Starret Thickness Gage Set Review (31 Leaves)
The Starret thickness gage set is one of those tools that represent American manufacturing. The feeler gauge is made from very high quality tempered steel and offers a ton of leaf thicknesses. Each feeler leaf is accurately cut and has a well rounded end. It is also very flexible and well-tempered to avoid breaking or bending permanently. The gauge body, on the other hand, is hardened to securely protect the blades from impact inside the toolbox.
All the 31 gauge strips are held together by a locking device that can be tightened to securely lock the blades inside the steel body. The locking mechanism can also be loosened using the thumbscrew to allow the blades to be retrieved smoothly during use. Each blade measures 1/2″ by 3 1/32″ and the leaf thicknesses range from 0.0015 inches to 0.035 inches covering the most useful sizes. The thickness size is laser-printed on one side, making leaf selection very easy.
- Has a ton of blades to suit many applications
- Leaves are well-tempered and don’t bend
- It is an American piece!
- Quite expensive
Bottom line, the starret feeler gauge is perfect for measuring thickness of clearances. Its price, however, is quite restrictive but its accuracy is unquestionable making it an ideal thickness gauge for pro-engine builders and machinists or regular mechanics. Like the other steel feeler gauges, the starret should also be soaked in light oil to prevent rusting. This simple care will make it last a lifetime with regular use.
Precision Feeler Gauge Review – 32 blades
The precision feeler gauge features a set of 32 blades bound together by a screw and nut within a blade protector. The protector is made of stainless steel and has a small thumb notch to aid removal of blades, just like the other thickness measurement sets reviewed so far. Although this Precision thickness gauge kit has little gauges that only measure 3.5 inches in length, it is good enough to get most of the gap measuring job done.
Notably, one of the feeler leafs is made of brass while the others are made of 65 manganese steel. This brass thickness gauge, also called non-ferrous blade, is useful for adjusting the electronic ignition – air gap on some old car models. The other blades can be used to measure clearances of engine valves and for other common applications such as measuring spark plug gaps, piston ring gaps, and the gap between the curvature of the fretboard and neck when tuning a guitar.
- Gauges are highly foldable
- Manganese steel feelers are resistant to abrasion
- This thickness gauge tool rusts very quickly if it is not properly oiled.
The precision gap gauge is good for measuring valve clearances and doing other general purpose uses. It is ironically not ideal for high precision work like machine work due to the inconsistent thickness of blades. When the blades are measured with a micrometer for accuracy, some happen to have an error margin of up to 20 microns. Other than that, this thickness gauge is nice and compact with a variety of feeler blades to suit your need.
ABN Angled Feeler Gauge Review – 16 pieces
ABN offset feeler gauge set is one of the most useful thickness measurement tools you can acquire for less than $10. This kit has slightly over a dozen angled feeler leaves each laser etched with the metric and decimal thickness size. These 0.5 inch wide blades are held together within a stainless steel blade protector using a nut and a screw. This locking mechanism makes it easy to swivel out the leaves for use and lock them back in for storage. The blade protector also has a notch that makes it super easy to retrieve the blades one by one.
The most noteworthy feature of the ABN gap gauge is the angled design of its tempered feeler leaves. This design makes the gauge tool good for valve clearance adjustment on engine compartments that are cramped for space. I found this feeler set very useful for checking the gap on lifters in flat engines such as the subaru boxes engine.
- Angled blades are good for accessing tight spaces
- Feeler gauges may rust if not oiled properly
ABN angled feeler gauge is an accurate and versatile gap measurement tool. You can use it to measure the clearance of engine valves in very tight spaces, gapping spark plugs, or setting neck relief on a guitar. ABN offset gauge is also inexpensive and very durable if maintained properly by applying a light layer of oil on the blades to prevent rust. You must also carefully unscrew the locking mechanism carefully to avoid losing the locking nut and the blades.
Hotop Feeler Gauge Kit Review – 32 blades
Hotop feeler gauge is one of the gauge kits with the most leaflets. It has 32 high-carbon spring steel thickness blades held together inside a blade protector. To keep them from falling, the protector has a lock nut for preventing the blades from falling apart in the tool box. Each blade measures 1/2 inch wide and 3 1/2 inches long and has both empirical and metric size etched on one side.
Out of 32 leafs, one is made from brass. This brass feeler is used to measure thickness where there is a magnetic field because it won’t stick on the magnet. A good example of where the brass blade can be applied is in setting the magneto gap on a small gasoline engine.
- The multiple blades increase tool’s versatility
- Super cheap
- Brass leaf enables the thickness gauge to be useful where there is magnetic field.
- Susceptible to rust if not oiled
- All blades but brass stick to magnet
The hotop thickness gauge set is one of the cheapest feeler gauges, costing less than $10. It is also very versatile because of the many leaflets. Furthermore, you can use the Hotop feeler gauge in both magnetic and non-magnetic environment. The only downside with this kit is the fact that the blades are not stainless steel. They are made from high-carbon steel except for the brass blade. This means that you must oil this feeler set properly before storage or the blades will rust.
Having said that, if you are looking for a cheap and accurate feeler gauge for setting the coil in your lawnmower or trimmer, for setting valve clearances, or gaping spark plugs, the Hotop set is a great budget option. I have one that I use in my auto repair projects and it serves me well.
How to use a feeler gauge to measure a spark plug gap
Time needed: 2 minutes
The following is an easy step-by-step procedure for using a feeler gauge tool to measure narrow gaps.
- Identify the spark plug that needs to be measured
The first step in measuring clearances or gaps is to identify the exact place or object that you need to measure. It could be a valve clearance, piston ring end, spark plug gap, or the surface of a cylinder head. In this case, we want to measure the gap between the ground electrode and center electrode of a spark plug, otherwise known as the spark plug gap.
- Check the specification sheet or repair manual
After identifying the place that needs measurement, check the specification sheet or manual for the correct measurement. For example, unless otherwise indicated, the gap between the ground electrode and center electrode of a spark plug should never exceed 0.055 inches. You can check gapping specifications on product manufacturers website as well.
- Choose the appropriate set of feeler gauge leaves
Knowing the right size of a gap helps to choose the right set of feeler gauges. The best feeler gauge is one that has at least the desired measurement. For instance, if you are measuring a very tight gap (say in the range of a thousandth of an inch), such as the flatness of a transmission steel plate, you need a gage set that at least has a leaf of that size. For larger gaps, you can always stack together a couple of blades.
- Slide the wire gauge, blade, or stack of feeler blades into the gap
To measure the clearance between two objects, slide the wire gauge or the calibrated blade into the gap. If the wire or blade slides freely, select the next measurement up and if it is snug, choose the next gauge down. You should feel a drag or a slight grab when you move the proper gauge back and forth through the slot
- Read the feeler gauge
Feeler gauges are easy to read. Each blade or wire gauge is labeled with its respective metric or imperial size measurement or both. If you are using a single gauge, just read the measurement on it. Otherwise, if you have stacked together two or more blades, just add together the different sizes to get the right measurement.
- Oil and keep the feeler gauge in a safe place!
Because a feeler gauge set has very delicate leaves, you need to maintain and store it carefully. The first step is to apply some lube generously to prevent rusting. You can use your favorite lube. Then, store the gage set in an air-tight container or enclosure. This helps prevent moist air from entering thus keeping the thickness gauge free from rust. I prefer to use a ziplock bag because it is easy to remove air from inside before sealing. Keeping the blades from rusting not only makes the gauge set last longer but also allows you to swivel the blades out smoothly. Also, ensure that the thumbscrew is snugged properly to hold the blades together. For a round wire type feeler gauge, hang it securely on a tool wall after oiling.