Best Spark Plug Gap Tools: Properly Adjust Your Spark Plug Gap

Re-gap your spark plug with these top spark plug gap tools

byLinsay Thomas, Norah Tarichia|
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BYLinsay Thomas, Norah Tarichia/ LAST UPDATED ON August 6, 2021

The spark plug gap is where the discharge that ignites the engine’s air-fuel mixture comes from. Your factory spark plug may come preset by the manufacturer, but you need to gap most aftermarket replacements. Our buying guide includes some of the best spark plug gap measuring tools that will help you get the correct gap size.

Best Overall
OEMTOOLS Blade Master

OEMTOOLS Blade Master

A high-quality feeler gauge with several blades that helps with measuring and adjusting the gap size.
Features 26 blades. Ergonomic design. Accurate measurements. Made of durable hardened steel. Easy to clean. Well-calibrated blades. Easy to use. Includes both SAE and metric sizes.
May come apart when dropped. The blades may rust. Needs lubrication.
Best Value

CTA Tools Spark Plug Gapper

A ramp-type spark plug gap measuring tool with an easy-to-read scale.
Cheap. Gives clear measurements. Includes inches and millimeter readings. Flexible. All-steel construction.  Allows for quick adjustment of spark plug clearance.
May not be as accurate as advertised. Cheap quality. Not eco-friendly.
Honorable Mention

CTA Tools Spark Plug Gap Gauge

A wire-type spark plug gap tool designed to give accurate gap measurements.
Can adjust iridium and platinum plugs. Durable, all-steel construction. Measures a wide range of sizes. Flexible. Laser calibrated in inches. Easy to read.
Fragile wire rings. You may get a misaligned tool. You may have to reassemble it.

Why Buy A Spark Plug Gap Tool?

  • Achieve better spark plug performance. The size of the gap of a spark plug determines its firing performance. The gapping tool will help you manually open the gap to the exact factory measurement recommended in your owner's manual. That way, you boost the efficiency of the spark plug in putting out a large enough spark to ignite the air and fuel mixture in your engine.
  • Correctly gap your new spark plug. Your original spark plug may come pre-gapped by the manufacturer. These plugs have a designated ignition gap, heat range, and torque that works for your engine. A new spark plug may not have the same gap size, and if you install it with a smaller or larger gap, you may notice a significant decline in your engine’s performance.
  • Prevent burnt electrodes. Used spark plugs may have a slight discoloration at the electrode (negative probe). Further inspection may reveal that the gap between the ground electrode and the center electrode is wider. If the gap is not properly aligned, the electrode will continue to discolor and will eventually burn away. 

Types of Spark Plug Gap Tools

Feeler Gauge

A feeler gauge is made up of a collection of calibrated metal strips of varying thicknesses. The blades look like a pocket knife when joined together. It's the best tool for measuring and adjusting the spark plug spacing. It’s easy to tell the difference in the blade sizes, and you can easily tell which gap size you are setting your plug gap to. Moreover, feeler gauges are inexpensive, and you can easily replace them in case you lose or bend them.

Ramp Style Gauge

A ramp-style gauge is similar to a silver dollar with size markings running around the edge of its face. The outer edge is the thinnest, and the gauge gets slightly thicker as you move to the middle of the tool. They are the least expensive and most convenient type of gauges since you can resize the spark plug gap and bend the electrode with them. However, they aren't as easy to read as feeler gauges, and they may have accuracy issues since the edges may bend or curve. 

Wire-Loop Style Gauge

A wire-loop gauge also looks like a silver dollar coin with the difference being that the outer edge has several wire loops of different thicknesses. It may have a hook (electrode tool) that helps you bend the electrode on the plug. These gauges are just as accurate as feeler gauges and can be used without the help of other measuring instruments just like ramp-style gauges. A wire-type gauge is typically accurate but isn't the best for measuring a spark plug with an odd gap size since it has a limited number of loops.  

Top Brands


CTA is a specialty tool manufacturing company that was founded in 1978. It originally started as a distributor of hand tools for other companies but then started making its own tools, which are sold throughout the world. The company produces more than 1,000 tools, including wrenches, spark plug sockets, valve spring compressors, and measuring gauges. Some of its best spark plug gap measuring tools are the CTA Tools Spark Plug Gapper and the CTA Tools Spark Plug Gap Gauge.

A&E Tools

A&E tools have more than 80 years of experience in the production of aftermarket automotive accessories. From its headquarters in Racine, Wis., the company supplies the industry with top-notch scanning tools, ratcheting wrenches, locking pliers, battery tools, and measuring gauges. One of its best-selling spark plug gap gauges is the A & E Hand Tool Spark Plug Gap Gauge.


Proto is a Connecticut-based manufacturer of hand tools. It’s a subsidiary company of Stanley Black & Decker, which was founded in 1907. Proto was the first-ever company to make the combination wrench, and some of its other products include ratchets, adjustable wrenches, and spark plug gap adjustment tools. One of its best-rated spark plug calibration tools is the Stanley Proto Spark Plug Gap Set.

Spark Plug Gap Tool Pricing

  • Under $5: Most gapping tools are generally inexpensive, and most of the products within this range do not compromise on accuracy. However, only a few offer both the metric and SAE measuring system. Expect to find mostly ramp-style gauges within this price range.
  • Over $5: This price range holds all types of measuring tools featuring high-quality steel constructions and easy-to-read measurements. Your decision will largely depend on the tool’s measuring size range and ease of use. 

Key Features


Select a measuring gauge that’s calibrated in the measuring system that you are most comfortable using. You can get one that has both millimeter and inch markings if you don’t want to bother with the conversion. Select one that offers a size range that’s similar to the gap size of your spark plug for utmost accuracy.


The best measuring tools are made of heavy-duty steel construction. They are good enough for measuring iridium and platinum plugs. Steel is strong and more resistant to corrosion. However, there are some steel gauges that may rust with time. You need to get a product from a well-known brand to make sure that you are paying for a quality product that won’t curve, rust, or corrode at the edges.


The best measuring tools have laser-etched markings on the steel. They are easier to read and do not fade out with time. It’s also easy to tell if you are getting the precise measurement since the exact size you need is dented in the steel. You can match it to the gap without using a marker to indicate the points.

Other Considerations

  • Flexibility: The measuring instrument should be flexible enough to allow you to change from one measuring size to another with ease. The most flexible tools are feeler gauges since blades of different sizes can be pulled out, pushed back, and interchanged with ease. 
  • Ease of Use: Choose a measuring tool without a complex design. You should ideally know how to set the measurements and set it on the gap or electrode to increase or reduce the gap, respectively. Wire-type gauges are easy to use since you only have to rotate the gauge when measuring.

Best Spark Plug Gap Tool Reviews & Recommendations 2021

The OEM Tools Blade Master has 26 calibrated blades that can measure sizes ranging from 0.0015 to 0.025 inches. You can get the exact value of the gap in either SAE or metric system (inches and millimeters). The measurements are laser etched in the middle of each blade. The blades are made of hardened tempered steel, which is long-lasting and resistant to rust and corrosion.

The blades are held together with a thumb notch for easy removal of each piece. The entire blade set maintains a neat and professional look due to the chrome-plated finish on each blade, which is easy to clean. The blades have smooth edges, and all 26 blades only weigh 3.2 ounces. That’s easy to carry around in your pocket or in a toolbox.

Despite being made of steel, these blades can rust when stored in humid conditions. You may notice that the blades are oily upon delivery, and you need to keep on lubricating them to prevent rust. Also, the blades may come apart if dropped. You may have to tighten the thumbscrew to keep the blades intact.

The CTA Tools Spark Plug Gapper has a heavy-duty construction built for strength and durability. It’s made up of a die-casted metal to harden the steel and increase the accuracy of the unit. It can be used for measuring and readjusting the spark plug gap. The gauge is calibrated in the imperial system, and the size markings are laser etched on the rugged steel construction.

The sizes range from 0.02 to 0.1 inches with 0.01 increments, and they are easy to read. The gapper is also designed with a key ring hole or a spark gap opener with a 7/16 inch diameter. The hole helps you accurately resize spark plugs with an electrode tool included. The tool can measure the clearance of any spark plug model.

However, this gapper may not be as accurate as advertised, and it may not give precise measurements for reducing the size of the spark plug. You may have to use another tool to confirm the small differences in values. Also, it’s made of cheap quality steel that may rust, and the size markings may fade with time. The products also contain harmful chemicals known to cause reproductive harm by the state of California.

The CTA Tools Spark Plug Gap gauge is made up of a strong and durable all-steel construction built to resist corrosion. It’s a circular gauge with easy-to-read, laser-etched sizes on its body in sizes ranging from 0.025 to 0.060 inches with 0.005 increments. Nine wire rings on the gauge's outer edges help you to accurately measure, increase, and decrease the gap size.

This CTA gap adjustment tool only weighs 1.44 ounces and will offer over 30 accurate gaping measurements before you need to readjust it. It also includes one electrode-adjusting tool. The unit is designed to adjust the plug without pressuring the center electrode. The tool can be used at home and in a professional garage.

However, a major downside with the product is its construction. The wire rings are fragile and may bend after about 25 measurements. Also, you may receive an inaccurately calibrated product upon delivery. The measurements may be 180 degrees off, and you may have to unscrew and reassemble the tool for accurate measurements. 

This spark plug gap gauge is circular and has easy-to-read markings. The tapered hole adjusts the electrode. The tool is made to comply with industry standards and is designed by Performance Tool, a Wilmar Corporation brand. This reliable gauge measures SAE sizes from 0.02 to 0.100 and metric from 0.5 to 2.5 mm.

This tool works as advertised, and it's useful if you want to check the measurement on pre-gapped plugs. It is easier to use than some rival brands, and the edge is sturdy, not flimsy. This type of gauge is handy because you can simply slide the plug around the ramp and stop at the proper gap and then pull the plug off.

However, you may have to scrape the label off the gauge in order to get an accurate reading. Also, it may not be the best option if you need to gap iridium plugs. Another problem is that it’s so small you may easily lose it.

This universal spark plug gauge is available in black or orange with a hard plastic handle. It covers a range of 0.20 inch to 0.08 inches, and metric measurements are featured on the reverse side. The scale can accommodate older vehicles as well as later model vehicles and even those with distributorless ignition systems. The gauge has a recess to adjust electrodes, and it comes with a pocket clip, so you can have it nearby at all times.

This tool makes gapping plugs a lot easier compared to tiny plug gapping tools, and you can get a good grip on what you're doing. It's a simple but functional device, and it's comfortable to use with no rough edges. The gauge is also very accurate, and the adjustment hole is useful for widening the gap. It is also simple to make small adjustments because it provides a lot of leverage, so you don't need to press very hard.

One downside is that there may be little bumps or imperfections on the tool's metal edge. Also, some users prefer standard round/coin-shaped spark plug gap tools, and the chrome coating may flake off after a short period of use.

This wide gap wire spark plug and gauge tool has eight round wire blades and is designed for use on new vehicles with high-energy engines. The device accurately sets spark plugs and comes with an electrode tool. The SAE sizes are: .025, .030, .035, .040, .044, .054, .060 and .080 inches, and the metric sizes are: 0.635, 0.762, 0.889, 1.01, 1.11, 1.37, 1.52 and 2.08 mm.

This tool is practical and well-made. It makes gapping your plugs quick and easy and is also handy if you just want to check them. It has a good range of gapping ability and is a good value for the price. Overall, it does everything a spark plug gap tool is supposed to do.

However, there have been some complaints that the gauge is a little flimsy. For example, the gapping portion is sheet metal that bends very easily. Some users have bent the gap tool while adjusting a plug.

This ramp-style spark plug gap gauge measures gaps from 0.020 inches to one inch (0.50 to 2.5 mm), and the measurements are stamped on the front and back. The hole operates as an electrode adjuster. You can also attach this gap gauge to your keychain for easy access.

This classic gap tool does the job efficiently. It works exactly as advertised, is very inexpensive, and is very effective. The engraving is solid, so it won't wear off very easily. It also has a great range, and it's simple to store when not in use.

Some users, however, prefer older-style feeler gauge blades. Also, it may not be the best option if you need to gap precious metal plugs with newer fine wire electrodes (compared to OEM plugs). It could potentially damage a fine wire platinum or iridium tip when attempting to adjust or measure the gap.

This spark plug gap tool has eight bent wire gauges with the following sizes: .022-inch, .025-inch, .027-inch, .028-inch, .030-inch, .032-inch .035-inch .040-inch. It also has the metric equivalent. The device is made in the United States.

This wire-based gap tool has increments that are easy to use to verify the gap. If the wire gets in, then it needs to be gapped smaller, and the adjustment tool makes it simple. The gauge also prevents damage to the soft metallic posts of the plugs. It's a good-quality tool and is a great option for a DIYer.

One downside is the plastic ends the wires go into are not the best quality. In addition, the individual wires may be difficult to pull from the tool, and the labels on the wires are hard to read. There have also been some complaints that it doesn’t feature a .020-inch gauge.


  • Handle your spark plug with care when cleaning or installing it. Dropping or mishandling the spark plug could reduce the gap size. Clean the spark plug with quick-drying alcohol (90 percent) and a soft brush before adjusting the gap size. 
  • Spark plugs usually have a build-up of white soot on the electrode, which can reduce the size of the gap. If you notice black soot on the electrode, consider buying a new spark plug, since that one has burnt out. 
  • You shouldn't use too much pressure while bending the electrode. It can be quite delicate and may fracture if bent by more than 0.2 inches with a single push. A fractured electrode may cause engine misfires. Also, be careful not to damage the core (center of the plug) to avoid buying a new one.  


Q: What happens if I don’t gap my spark plugs?

A: You may end up with a gap that’s too close and may not deliver the right amount of spark to combust the air-fuel mixture. If that happens, the engine may ignite too soon or skip firing. The spark plug won’t remove the excess heat from the cylinder ignition chamber and transmit it to the engine’s cooling system. If the gap is too wide, the spark plug may not fire at all.

Q: How do I know if the gap needs readjusting?

A: You need a measuring tool with the original gap size for your spark plug. Try and insert the measuring tool in the gap, and if it's a perfect fit, you don't need to readjust the hole. If the measuring tool goes through and leaves some space, then the hole is too wide. If it doesn't go through, then you need to reopen the hole to match the tool size.

Q: Can I use two blades to adjust the gap size?

A: Only if your spark plug has a big gap size, such as 0.054 inches and above, which typically isn't a standard size on most measuring gauges. You can use thin blades of different sizes to get the accurate size of the gap. Just be careful not to break the electrode, since using double blades increases the strength of the tool. 

Q: Do I have to replace the measuring tool every time I replace my spark plug?

A: To maintain accuracy, it’s best to replace the measuring tool, especially if you have used it for over 20 measurements. The measuring tool may wear out, curve, or get corroded on its edges, which significantly reduces its accuracy. 

Final Thoughts

Our top pick is the OEMTOOLS Blade Master. It conveniently comes with a penknife design filled with 26 blades of different thicknesses, which will help any professional mechanic to re-gap spark plugs of different sizes. You can also use two blades at the same time if you have a spark plug with an odd gap size.

If you need a cheap yet accurate measuring and adjusting tool, then consider the CTA Tools Spark Plug Gapper. It’s a key-chain measuring tool that offers more than 15 accurate measurements.

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