For as small as it is, the gap at the tip of your spark plugs is one of the most important features of your engine. If you want to be able to adjust this in your own garage, you want to get the best spark plug gap tool for the DIY mechanic.
Spark plug gap tools come in a few popular styles. All of them have distinct pros and cons. Even though these are relatively common tools, they’re not as easy to find at auto parts stores as you might expect. When you’re shopping for a spark plug gap tool, AutoZone is less likely to have the answer than Amazon.
That’s why we’ve rounded up our top 5 spark plug gap tools here. There are several different styles represented on our list. Not everyone will be the right choice for your car, so read through the reviews before you decide which one is the best spark plug gap tool for you.
Top 5 Best Spark Plug Gap Tool Reviews
01. Hotop Steel Gap Measuring Tool
If you’re looking for a comprehensive tool that can measure any spark plug gap, you’ll love this steel gap measuring tool from Hotop. It gives you 32 precise measurements, ranging from a width of .04 to .88 mm. The blades also include imperial measurements, making this tool incredibly versatile.
The design of the Hotop gap measuring tool is smart. The blades tuck together into a slim, compact casing. The entire thing weighs less than 5 ounces, so it’s very portable. The non-slip nut and anti-corrosive coating make it very durable, too.
While this Hotop tool is excellent for measuring spark plug gaps, it’s not the most delicate tool for adjusting them. It will work fine on older-style copper spark plugs, but you certainly don’t want to use it to adjust iridium spark plugs or other more fragile designs.
Like with any spark plug measurement tool, there is a slim margin for potential error in the measurements. For the price, though, this tool is quite accurate and a very useful tool to have in your garage for more than just adjusting spark plugs.
Highlighted Benefits
- Includes 32 blades to accommodate a range of gap sizes
- Durable Manganese steel construction
- Folds up to fit easily into your pocket or toolkit
- Coated with anti-rust compounds to extend its life
- The slim margin of potential measurement error
02. Performance Tool W80535 Spark Plug Gap Gauge
This is the kind of tool you’re probably picturing when you think of a spark plug gapper. It’s a coin-style spark plug gap gauge that runs from .5 to 2.5mm. This basically runs the gamut of the gap sizes you’ll need. As far as portability, it’s small enough you can put it right on your keychain and not feel like it weighs you down.
The only issue with this style of gap gauge is that it can lead to uneven gap adjustment if you’re not careful. Since the outer edge runs at a gradual slope, pushing it too hard against the gap can tilt one side of the gap higher than the other.
Because of that uneven edge, the coin-style gap tool normally isn’t a good option for adjusting spark plug gaps. This one is different, though. It comes with a tapered hole you can use to adjust electrodes easily and safely. This addition makes this Performance Tools spark plug gauge the best spark plug gap tool you can get for such a low price.
Highlighted Benefits
- Can measure any size of the gap
- Etched-in markings are easy to read and won’t fade with time
- Includes an electrode tool for adjusting electrodes
- It can be carried on a keychain for easy portability
03. A&E Hand Tools E-Z Grip Spark Plug Gap Gauge
The A&E Hand Tools spark plug gap tool is an ergonomic and affordable all-in-one device you can use to measure and adjust spark plugs of all designs. Like coin-style gap tools, it has a graded edge that measures all the way from .02 inches to .08 inches, with marks for everything in between. This is a good range for both older and new vehicles. The flip side of the tool gives you metric measurements, as well.
The attached handle on this A&E spark plug gapper makes it very comfortable to use, whether you’re using it for measuring or gapping. It would be nice if it folded up. It’s still plenty lightweight and has an attached clip for easy carrying, but it will take up more space in your toolbox than other options.
Our favorite thing about this tool is the gap adjustment feature on the tip. This makes it easier for you to adjust the gap without accidentally touching the central electrode or surrounding porcelain. It’s this feature that earned the A&E E-Z Grip Gap Gauge a spot among our best spark plug gapper tools.
Highlighted Benefits
- Built-in recess for electrode adjustment
- Easy and comfortable to use
- Wide enough range for older and newer vehicle models
- Highly accurate measurements
- Markings are clear
04. Lisle Spark Plug Gauge Gap
Here’s another very affordable old standard. The pros and cons of this Lisle Spark Plug Gauge are about what you’d expect for any gapper tool of this style. The tapered edge measures smoothly throughout the width range in both imperial and metric systems. It also has a central hole that can be used to adjust electrodes.
The most notable thing about this Lisle spark plug gap tool is that it gives you a wider measurement range than many options. It goes from .02 inches to .1 inches. No matter what kind of car you drive, the spark plug gap will be within this range. You can use this worry-free on any kind of vehicle.
One great thing about this style of spark plug gapper is that it’s virtually impossible to break. There aren’t any moving parts, and the markings are etched deeply so they won’t wear away from use. It’s not made of the hardest metal, but it’s plenty durable to withstand being thrown in your toolbox or carried on your keychain. And for just a couple of bucks, it’s one of the cheapest car repair tools you’re likely to buy.
Highlighted Benefits
- Compact and portable
- Built-in adjustment tool
- A wider range of measurements than many gap tools
- Deep-etched measurements won’t fade with time
05. CTA Tools 9 Wire Spark Plug Gap Gauge
Finally, let’s look at this wire-style gauge tool from CTA. This style of gapper was designed to be gentler and more accurate than coin-style gap tools. If you use iridium spark plugs, a tool such as this one is likely your best option for smooth and damage-free adjustment.
This CTA gap tool is very well-built. It’s all steel, so it won’t break, and it’s not likely to be damaged by rust. The wires are strong enough that they won’t bend or chip from normal use, though they are susceptible to breaking under enough pressure. The only part we’re not a huge fan of is the gap adjuster. It’s functional but feels flimsier than the rest.
As with most wire-style gap gauges, the main drawback of this CTA tool is that it only gives you 9 common gap width options. You’ll want to double-check your vehicle manual and make sure it has the one you need before you buy this tool.
For delicate spark plugs, the CTA 9-wire gap tool is a good option. It’s not as versatile as the other options on this list, but that may not be a problem for you if you’re only adjusting the spark plugs on one or two vehicles.
Highlighted Benefits
- Measures and adjusts without damaging electrodes
- All-steel build won’t break or rust
- Gap adjuster built-in
- Spot on accuracy
How to Gap Spark Plugs: Your Spark Plug Gap Guide
Once you’ve purchased your best spark plug gap tool, how do you use it? Gapping a spark plug is actually quite easy once you know the right process to follow.
- Every vehicle has its own ideal spark plug gap. You can find the correct gap for your car by checking your vehicle manual. If you don’t have your manual, you can find a spark plug graph for your vehicle’s manufacturer online. Find your year and model and the recommended gap. Typically the more power your engine produces, the smaller the gap that will be required. A larger gap requires more voltage from the ignition to make the spark jump across it.
- Check the gap in the spark plug using a feeler gauge.
- Choose the right wire for the size of the gap, then run the wire between the electrodes of the spark plug. If done correctly, the wire will catch on the electrodes as it passes.
- If you need to change the width of the gap, you can do so at this point.
- To widen the gap, hook the gauge onto the ground electrode. Tug it gently until you’ve widened the gap as much as you need to. Use caution in this step—you don’t want to touch the gauge to the center electrode or the porcelain.
- To narrow the gap, press the ground electrode against a soft, clean surface, like a towel laid on the ground. Do this gently so as not to bend or damage the electrode.
- Check the gap again with the feeler gauge. Ensure the gap is the correct width for your vehicle, and make further adjustments as necessary.
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Spark plug gap performance can be affected if you adjust the gap by more than .2 millimeters. If you do, the electrodes might not line up correctly. This is one reason you should make all your adjustments slowly and carefully.
The steps above are what you want to follow if you have standard spark plugs in your vehicle. If you use iridium spark plugs, though, you don’t want to use a standard gapping tool. The center electrode on an iridium spark plug is hard and brittle. Applying pressure to the electrode can fracture it.
If you’re wondering how to gap iridium spark plugs, follow the steps below:
- Check the factory-set gap on the spark plug’s packaging, and compare it to your vehicle’s specifications. In most cases, iridium spark plugs don’t need to be gapped. Iridium spark plugs are more efficient than other designs and can compensate for small variations. Don’t gap an iridium spark plug unless it’s off by a significant margin.
- Use a pair of needle-nose pliers to bend the ground strap up or down until it’s reached the correct height. Be careful not to touch the pliers to the center electrode or the surrounding porcelain. You can use some gapping tools for this but don’t use a round gapping tool, as this could damage the electrodes.
- Use a feeler gauge to measure the gap and make sure it matches your vehicle’s specifications.
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How to Gap Spark Plugs without Tool
As with the advice above, the first thing you should do is make sure you need to gap your spark plugs. If you bought spark plugs recommended for your vehicle, they’re likely gapped to the correct specifications already from the factory.
If it turns out you do need to adjust the gap, you don’t need to necessarily buy the best spark plug gap tool to do so. Needle nose pliers make a great homemade spark plug gapper. They’re the recommended spark plug gap tool for iridium, but they can also work for other spark plug styles.
The trickier thing is finding the right tool to measure the gap. Whether you measure your spark plug gap in mm or inches, it’s going to be a very small amount. You can use something thin and stackable, like strips of plastic sheeting, to determine the width of a correctly gapped spark plug, and use that for comparison. This is a less accurate way to measure than a feeler gauge, however. Since these tools are fairly cheap, you’ll likely be better served to buy a tool.
Things to Consider Before Buying Spark Plug Gap Tool
Spark plug gap tools are relatively simple by design, so you might not think there’s much to decide when you start to shop. The decision is a bit more complicated than you might expect, though. Not all spark plugs are designed to be the same. Measuring and adjusting your spark plugs correctly means getting the right tool for the job.
There are 4 styles of spark plug commonly in use today:
- Copper/nickel spark plugs. This is what people mean if they talk about the standard or normal spark plugs. These have an inner core of copper, with electrodes coated in a nickel alloy. They’re inexpensive and short-lived, especially in modern vehicles. The electrodes are solid, however, and can be measured and adjusted with any gap tool.
- Platinum spark plugs. These use platinum on the electrodes instead of nickel. Since platinum is harder than nickel, the spark plugs won’t wear away with use. This increases their average lifespan. Like standard plugs, these can be adjusted with a variety of tools without the risk of damage.
- Iridium spark plugs. Like platinum spark plugs, iridium spark plugs have a longer lifespan, but it’s for a different reason. Iridium allows better combustion than nickel. Iridium is more brittle, however, so you’ll need to use care when adjusting them. Wire-style gauges are a better choice than coin-style options.
- Silver spark plugs. Of all the plug designs, silver offers the most conductivity. It is not an especially durable metal, however, so like iridium, you’ll want to be careful when adjusting the gap. Silver spark plugs are rare in automotive applications. You’re most likely to encounter them on older European cars.
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There are other design elements that can affect how a spark plug responds to gapping. Spark plugs that have a “fine wire” core feature a thinner central electrode. This allows more metal to be put around it, conducting more electricity and making the spark plug more efficient. These thinner electrodes are more susceptible to damage, however.
If you’re using fine wire spark plugs, get a wire-style or feeler gauge gap tool. These designs let you put pressure only on the tip, without pressing on the delicate central electrode.
Which style of spark plug your vehicle uses is the most important thing to consider before you buy a gap tool? Generally speaking, copper spark plugs are the most common—there’s a reason you’ll hear them referred to as “standard.” This is shifting more with newer vehicles, however, which are designed to use more efficient iridium or platinum spark plugs.
Spark Plug Gap Tools FAQs
Does the spark plug gap have to be exact?
For most spark plugs, yes, you need to make sure the spark plug gap exactly matches the specifications in your manual. It’s also important to make sure all of the spark plug gaps match each other across all of your cylinders. Issues with your spark plug gaps can lead to misfires and other engine issues, so it’s not something you want to mess around with. The exception to this is iridium spark plugs, which are more efficient and can accommodate slight variances.
What should the spark plug gap be?
The correct spark plug gap varies from one vehicle to the next. The ideal spark plug gap for most engines is between .75mm and .8mm. Your vehicle’s manual will give you the correct measurement for your engine.
How do you use a wire spark plug gap tool?
These tools are different than the old coil-style gap tools. They have wires of different widths along their lengths. You can use these to determine how large the gap is with more precision and delicacy than coin tools. They also often have components designed to widen the gap gently without touching the porcelain or center electrode. The only disadvantage of wire spark plug gap tools is that they only include a few common gap sizes, unlike coin tools, which can be used to measure any spark plug.
What happens if the spark plug gap is wrong?
An incorrect spark plug gap can cause engine issues. If the gap is too narrow, there’s not enough room to generate a hot spark. This means the air/fuel mixture never ignites. You’ll likely notice your car idling rough, and the spark plug will be blackened or shiny with fuel. If the gap is too broad, the spark has to travel too far. This is more likely to result in failed starts and misfires than a gap that’s too narrow.
Can the wrong spark plug gap cause a misfire?
Gap problems aren’t the most common cause of misfires, but they can contribute. This is especially common as the spark plugs age since the gap naturally widens over time as a result of wear.
Final Words
Gapping your spark plugs is a delicate and often necessary procedure. Getting the right tools for the job is imperative if you want to do it correctly and avoid engine damage. There’s no one right answer when you’re looking for the best spark plug gap tool. It really depends on what kind of spark plugs your car uses.
For copper spark plugs, a coin-style gauge tool like the Lisle Spark Plug Gauge Gap is a time-tested way to get accurate measurements and make smooth adjustments. For more delicate iridium spark plugs, the Hotop Steel Gap Measuring Tool or CTA Tools 9 Wire Spark Plug Gap Gauge can be the best spark plug gap tool for the job.
Whichever one you choose, any of the tools above is a durable, convenient way to measure your spark plug gaps. We hope this guide has helped you hone in on the right one for you.
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