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Last updated on September 6th, 2021
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 of such a system is a car engine.
An engine has several parts that seem flush or in contact with each other when observed. However, when you check with a precision tool such as a feeler gauge or micrometer gauge, you find very tiny gaps. In some cases, these small clearances are part of the design and must be retained for the system to work properly. In other cases, the tiny gaps need to be identified and eliminated completely. For example, the valve clearance gap in a car or motorcycle engine must be maintained for optimal engine performance. On the other hand, the cylinder head surface must be resurfaced during an engine rebuild exercise to ensure the head gaskets seal properly to prevent overheating.
In short, micro gaps matter so much in complex systems and can make a very big difference. That’s why there are precision tools such as feeler gauge kits and micrometer screw gauges for measuring very small gaps with more accuracy.
What is a Feeler Gauge?
A feeler gauge is a precision-measurement tool for measuring the thickness of very narrow gaps using very thin blades. You cal also use the tool to measure the flatness of surfaces. A feeler gauge kit consists of a stack of metal blades of different calibrated thicknesses.
To use it, you slide a blade or a stack of them through the gap you want to measure until there is a slight grab. Then, read out the thickness value from the blade or add them up if you have used a stack of blades. The value you get is the precise size of the gap.
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 feeler Gauge
As the name goes, steel thickness gauge sets are made of steel. However, carbon is added to the feeler blades to increase their strength and flexibility. Some steel feeler blade tools are made of alloys of manganese while others are stainless steel. Comparatively, stainless steel feeler gauges better quality than other steel feeler gauges, mainly because they do not rust. The others rust very quickly in humid conditions. That is why you have to keep them oiled in an airtight enclosure.
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 means that the brass feeler blades cannot stick on magnets. Therefore brass thickness gauge kits are suitable for applications where there is a magnetic field.
You can use a brass feeler gauge to set the air gap between the reluctor sensor and trigger teeth when configuring the engine cam. Other applications of brass feeler gauges include setting the air gap in electronic ignition, harmonica repair, harp repair, and setting the air gap on a distributor.
Furthermore, brass thickness guages can also perform the ordinary tasks of a feeler gauge. In fact, one of the advantages of using the brass kit is that it does not rust. So you do not need to drench the feeler blades in oil as you would with steel blades.
3. Round Wire Feeler Gauge
A wire-type feeler gauge is also known as a gapping tool or a gap gauge. It has the shape of a round coin with wire loops of different calibrated sizes on the circumference. Although it can be used like other feeler gages, a wire gap gauge is ideal for gapping spark plugs. It is typically small in size and has a limited number of gauge sizes, making it unsuitable for other general applications. However, despite the limitations, round wire gap gauges gap spark plugs more easily than feeler blades. My favorite wire gapper is the CTA Tools 3238 9 Wire Spark Plug Gap Gauge. The unit can measure 9 different sizes and has a built-in spark plug gap adjuster.
Amongst the brass and steel thickness gauge kits, there are those with short or long blades, others have tapered blades while others have angled blades. These different designs on the blades target specific applications. For example, an offset feeler gauge is suitable for use in tight spaces because it provides good visibility of the workpiece. In contrast, straight blades are suitable for spacious workspaces where visibility is not a problem.
In this article, I will share with you the 5 best feeler gauge sets you can count on for your precision measurements. It does not matter if you want to adjust valves in your motor, gap spark plugs, or tune a guitar. This selection of thickness gauge tools will not disappoint you. They are versatile and you can use them in multiple applications. Read on to find out more.
Our Top Picks
|Proto feeler gauge J000TL||starrett 66b thickness gauge set||Precision Feeler Gauges||ABN Universal Standard SAE and Metric Offset Valve Feeler Gauge||Hotop Steel Feeler Gauge|
|Buy from Amazon||Buy from Amazon||Buy from Amazon||Buy from Amazon||Buy from Amazon|
Proto Feeler Gauge Review (25 blade) – Best Overall
Proto feeler gauge set (J000TL) has 25 blades bound within a steel blade holder. The holder keeps all the blades together and protects them from damage. It has an adjustable thumbscrew that enables you to loosen or tighten the blades in place with ease.
The feeler blades are 12 inches long and 1/2 inches wide. They are laser-etched on one side in both empirical and metric units although the main scale is empirical. The blades are made from high carbon steel which is hard to break, does not deform easily, and is resistant to wear. This is why they last longer and keep their shape even after you bend them during use.
These super long feeler gauges can easily get into deep areas which makes them suitable for measuring gaps in hard-to-reach spaces. Furthermore, when the tips start to wear down, you can cut them off and still remain with adequate length to allow you to carry on with measuring. This adds to the durability and versatility of the proto feeler gauge kit.
- 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 the J000TL proto feeler gauge is a bit pricey, it is a high quality gap measurement tool from the U.S.A. It has a decent number of blades to get you through most micro gaps. The length of the blades is perfect for both general purpose use and long reach measuring. You can use it to measure the flange gap during pipe stress and valve clearances in deep places. You can also use it to measure the blower lobe clearance among other uses.
Starret Thickness Gage Set Review (31 Leaves) – Best for Automotive Applications
The Starret 66B thickness gauge set an American made feeler gauge. It has a total of 31 straight blades which are made from very high quality tempered steel. Each blade is accurately cut and has a well rounded end.
The feeler blades are flexible and well-tempered to avoid breaking or bending permanently. They are also protected from impact by a hardened steel body. The gauge body has a locking thumbscrew for holding all blades together. You can loosen it easily to retrieve the blades or tighten it to lock the blades in place.
The Starret feeler gauges measure 1/2″ wide by 3 1/32″ long and the thicknesses range from 0.0015 inches to 0.035 inches. The thickness of each blade is laser printed on the side in inches only. This enables you to select a blade easily from the bunch.
- Has a ton of blades to suit many applications
- Leaves are well-tempered and don’t bend
- It is an American product!
- Quite expensive
The Starret 66B feeler gauge kit is compact and has a look and feel of quality. It incorporates all the feeler blade sizes you would need for most applications. The blades are cut precisely to give you accurate measurements every time. Unfortunately, the kit has a premium price tag. This makes it unsuitable for DIYers but perfect for professionals like pro-engine builders, machinists, and regular mechanics whose jobs require more precision accuracy. The kit does not include a brass feeler leaf. Therefore, you would need to get a brass feeler gauge for use in magnetic fields.
Precision Brand Feeler Gauge (32 blades) – Best for guitar setup
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.
Although this Precision thickness gauge kit has fairly short feeler gauges (3.5 inches long) it is good enough to complete most of the gap measuring jobs.
Notably, the kit has one feeler leaf while the rest are made from 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 are general purpose. You can use them tot measure gaps in your DIY projects that involve tasks such as measuring spark plug gaps, measuring piston ring gaps, and finding out 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
- The blades rust quickly if you dont oil them properly.
The Precision Gap gauge is good for measuring valve clearances and doing other general purpose uses. Ironically, the unit is not ideal for high precision work like machine work due to the inconsistent thickness of blades. If you measure the blades with a micrometer for accuracy, you will notice some have significant error margins of up to 20 microns. Other than that, the Precision thickness gauge is nice and compact, and perfect for DIY projects. It is also inexpensive.
ABN Angled Feeler Gauge Review (16 pieces) – Best for valve adjustment
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 blades. It makes the feeler gauge kit perfect for adjusting valve clearances especially on engine compartments that are cramped for space. In particular, I found it convenient for adjusting valves on my subaru horizontal engine. The boxer engines of subaru vehicles does not provide good clearance for engine tuning and therefore an offset thickness gauge comes in very handy.
- Angled blades are good for accessing tight spaces
- Many feeler leaves provide versatility
- Feeler gauges may rust if not oiled properly
- Locking nut easily comes off
ABN angled feeler gauge is fairly accurate, versatile, and inexpensive gap measurement tool. It is perfect for measuring the clearance of engine valves in very tight spaces, gapping spark plugs. You can also use the kit for other gap measuring applications that don’t a lot of precision such as setting the neck relief on a guitar. The kit is durable only if you maintain it properly by applying a light layer of oil on the blades to prevent rust. You must also unscrew the locking mechanism carefully to avoid losing the locking nut and the blades.
Hotop Thicknesss Gauge Kit (32 blades) – Best for spark plugs
Hotop feeler gauge is one of the gauge kits many leaflets. It has 32 high-carbon spring steel thickness blades held together inside a blade protector. The protector has a lock nut that the feeler blades from falling inside the toolbox.
Each blade measures 1/2 inch wide and 3 1/2 inches long and has both empirical and metric size etched on one side.
One of the leaves is brass, which is good for measuring thickness where there is a magnetic field because it won’t stick on the magnet. A good example of when to use a brass blade is when 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 my favorite budget feeler gauge. It costs less than $10 and has very many strips including a brass blade. The only major downside is that the blades are not stainless steel but high-carbon steel except for the brass blade. This means that you must keep them oiled before storage or they will rust.
Nevertheless, if you want a cheap, fairly accurate, and versatile feeler gauge for setting the coil in small gas engines, setting valve clearances, or gaping spark plugs, the Hotop feeler set is perfect. It costs less than $10 and does a great job. I have one that I use occasionally for auto repair projects and it serves me well. However, you have to keep it greased to prevent rusting.
How to gap spark plugs with feeler gauge kit
The following is an easy step-by-step procedure for gapping spark plug using a feeler gauge set. Ensure you have the following items before you begin
- Spark plug
- lubricating oil
- Feeler gauge set
- Flat screwdriver
Time needed: 5 minutes.
Follow these steps to measure and gap the spark plug of your internal combustion motor.
- Identify and access the spark plug that needs gapping
The first step is to pick the spark plug you want to gap. If you have not removed it from the engine, this is the right time to do so. Get a 3/8 inch ratchet and a deep socket to remove the spark plug from the engine. Most spark plugs require a 16mm socket. Even when working on other things such as valves, piston ring end, guitar, or cylinder head, the first step should always be to identify and access the item.
- Check the specification sheet or repair manual
After getting ahold of the spark plug or whatever it is you want to measure, find the specification sheet or repair manual to get the correct measurement specifications. If you cannot find it, ask the experts. The disadvantage of this approach is that you might not get the exact values. For example, an expert will tell you that the gap between the ground electrode and center electrode of a spark plug should not exceed 0.055 inches. They hardly give you specific measurements. For this reason, I suggest you first check even with the product manufacturer before going to the forums.
- Select the right size of the feeler gauge leaves
Now that you have the right gapping specification, choose the appropriate size of feeler leaf. If you cannot find a single leaflet for the gap size, stack two or more feeler blades together to attain the gap size.
- Measure the gap by sliding the feeler blade(s) between the spark plug electrodes
Try to slide a feeler blade or blades (if you have stacked two or more) through the spark plug gap. This is the gap between the center and ground electrode. If the feeler leaf slides freely, select the next measurement up. If the blade fits snugly, choose the next gauge down. Try to stack two or more blades until you feel a slight drag. This should be the size of the spark plug gap. Now proceed to the next step.
- Read the feeler gauge value
To determine the size of the gap, read the measurement on the feeler gauge leaf. If you have stacked two or more blades, add together the measurements. Be careful to choose the same unit of measurement because most feeler gauges have both metric and imperial size labels. For example, I used two feeler blades of size 0.04mm and 0.088mm which should add up to 0.092mm. If the measured value is within 0.03 inches of the reference value, the spark plug is properly gapped. Otherwise, jump to the next step.
- Narrow the spark plug gap if it is wider than the specified value
If the feeler gauge reading is bigger than the specified gap size, tap the ground electrode slightly to narrow the gap. Use a lightweight object such as a spanner or pliers. Alternatively, tap the ground electrode slightly on a hard surface to narrow the gap. Repeat step 4 to verify that you have properly gapped the spark plug.
- Expand the spark plug gap
If the thickness gauge reading is smaller than the reference value, you need to expand the spark plug gap. Gently pry the ground electrode slightly to expand the gap. Measure the gap again until you get the right size. A wire gap gauge is the best tool for this job because you can use it to measure and expand the gap more precisely.
- Oil and keep the feeler gauge kit 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 to keep it away from moist air. Moist air promotes corrosion and may cause the leaflets of your feeler gauge to rust. I prefer to use a ziplock bag because it is easy to remove air from the inside before sealing. Keeping the blades from rusting not only makes the gauge set last longer but also allows you to swivel the blades in and out smoothly.
Lastly, ensure that the thumbscrew is snugged properly to hold the blades together. For a round wire type gap gauge, coat it with a layer of lube and hang it securely on a tool wall. These simple maintenance tips will make your gap measuring tool last longer.
How to gap spark plugs with Hotop Feeler Gauge – VideoThis is a step by step video for checking the gap of a spark plug using Hotop thickness gauge and gapping it appropriately.
Frequently Asked Questions
There are three broad categories of feeler gauges, namely brass feeler gauge, round wire feeler gauge or gap gauge, and steel feeler gauge. However, there are other subcategories based on design such as straight and offset thickness gauges.
You can adjust valve clearance without a feeler gauge but you will not get the size of the clearance gap correct.
A feeler gauge can cost as low as $5 and as high $100. It all depends on many factors including the quality of material used, place of manufacture, and the number of blades.
You slide feeler blade(s) between the center electrode and ground of a spark plug to measure the spark plug gap.
A gap gauge is a small precision tool that uses round wires of known size to measure the spark plug gap. In contrast, a feeler gauge uses feeler blades or leaves.
0.04 the size of the the smallest feeler blade in millimeters. It is the equivalent of 0.0015 inches.
To maintain a feeler gauge set you only need to wipe each blade dry after every use and apply a layer of lubricant. It does not matter where the manufacturer says it is stainless steel. You just apply some lube and your thickness gauge set will thank you.
The least count on a feeler gauge that I have come across is 0.04mm or 0.0015 inches. It is thinner than the average thickness of a paper.
To check or measure the accuracy of a feeler gauge, you use precision tools such as a micrometer screw gauge. However, make sure the micrometer has a calibration certificate for accuracy.
The number on a feeler gauge blade indicates the size of the blade. Some feeler gauges are laser printed in either mm or inches while some have both measurement standards.