A spark plug gap tool checks the space between the center electrode and the side electrode of a plug. Most gauges are either a flat coin with a tapered edge, a set of round wires or a ramp that you slide the plug against. Many also include a small hole or notch for nudging the side electrode to open or close the gap.
The six tools below are small hand gauges, from a nine wire set to simple coin styles. Ranges, materials and weights come from each listing page and are the makers’ own claims. We have not used these tools ourselves. Where a listing disagrees with itself, we say so. Always check the gap figure for your engine in its own manual.
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What to Look For
| Feature | Why it matters |
|---|---|
| Gauge style | Coin, ramp and wire gauges read the gap in different ways |
| Range | The listed gap for your engine must sit inside the scale |
| Metric scale | Handy if your manual lists millimeters |
| Adjuster | A notch or hole lets you bend the side electrode with care |
Specs at a Glance
| Tool | Style and range | Material | Notes |
|---|---|---|---|
| CTA 3235 | Coin or ramp type; 0.020 to 0.100 in (title) | Alloy steel, plated | Weight listed as 0.27 g; M14 thread size listed |
| A and E 4450A | Gauge with pocket clip | Not stated | Metric scale on the reverse; electrode recess; 7.7 x 3.4 x 0.5 in |
| CTA 3238 | 9 wires, 0.025 to 0.060 in | Plastic holder | 2.25 x 2.75 x 6 in; 1.44 oz |
| OEMTOOLS 25352 | Ramp style; SAE and metric | Blend | Keychain hole; 30 day warranty; range figure conflicts |
| Lisle 67870 | Tapered edge gauge | Alloy steel | Flanged hole for the side wire; limited lifetime warranty |
| K Tool KTI73701 | Coin type, 0.020 to 0.100 in | Not stated | Increments of 0.001 in; storage hole |
The 6 Best Spark Plug Gap Tools
1. CTA Tools 3235 Spark Plug Gapper, Coin Style
A plated alloy steel coin style gapper whose title gives a 0.020 to 0.100 inch measuring range. The product details call it the original ramp-type version and list an M14 thread size. The listed weight is 0.27 grams, which looks like a typo, and the bullets stay general, so check the scale when it arrives.
Suits: a quick check in the garage. Strengths: a wide stated range from one coin. Weaknesses: thin listing detail and an odd weight figure. Skip it if you want a printed metric scale confirmed in the listing.
2. A and E Hand Tools 4450A E-Z Grip Spark Plug Gap Gauge
A flat gauge with a pocket clip, a metric gapping scale shown on the reverse side and a recess made for adjusting electrodes. The listing gives 7.7 by 3.4 by 0.5 inches and 0.8 ounces, and names China as the country of origin. The brand line in the table shows a different name from the A and E in the title, so the two names do not match.
Suits: a toolbox or a shirt pocket. Strengths: a clip and both unit scales. Weaknesses: no range or material is listed. Skip it if you need a stated measuring range.
View A and E Hand Tools 4450A E-Z Grip Spark Plug Gap Gauge , black on Amazon
3. CTA Tools 3238 9 Wire Spark Plug Gap Gauge
A holder with nine wires at 0.025, 0.030, 0.035, 0.040, 0.044, 0.045, 0.050, 0.055 and 0.060 inch. The listing describes heavy-duty construction and a plastic body of 2.25 by 2.75 by 6 inches. Wire gauges let the plug electrode drag on a round wire of a known size, which some people find easier to feel than a flat coin.
Suits: checking against common gap sizes. Strengths: nine fixed sizes. Weaknesses: no metric scale listed and no adjuster mentioned. Skip it if your engine calls for a gap above 0.060 inch.
View CTA Tools 3238 9 Wire Spark Plug Gap Gauge on Amazon
4. OEMTOOLS 25352 Ramp Style Spark Plug Gap Gauge
A ramp style gauge with SAE sizes stamped on the front and metric sizes on the back. The maker says the small hole can pull the electrode wider or press it closer, and doubles as a keychain eyelet. The bullet states a range of 0.020 inch to 1 inch (0.50 to 2.5 mm), which cannot be right, since 2.5 mm is about 0.100 inch. The warranty is listed as 30 days.
Suits: owners who switch between inch and metric manuals. Strengths: two scales and a keychain hole. Weaknesses: a contradictory range figure. Skip it if you need a clearly stated range.
5. Lisle 67870 Spark Plug Gauge Gap Tool
An alloy steel gauge with a tapered edge for gauging plugs and a hole with a flange that the maker says adjusts the side wire without pressure on the center electrode. The listing shows a limited lifetime warranty and a weight of about 22.7 grams.
Suits: careful side wire adjustments. Strengths: a purpose made adjusting hole and a longer warranty. Weaknesses: the listing gives no range figure. Skip it if you want a printed metric scale.
View Lisle 67870 Spark Plug Gauge Gap Tool on Amazon
6. K Tool International KTI73701 Universal Spark Plug Gap Gauge
A circular coin type gauge that measures in increments of one thousandth of an inch from 0.020 to 0.100. The maker says it gauges and gaps all types of plugs, has an easy to read scale and a punched hole for storage. The table lists the vehicle service type as UTV, so the wording on the page is not fully consistent.
Suits: a small, simple gauge for any plug. Strengths: a clear stated range and fine increments. Weaknesses: no metric scale is mentioned. Skip it if you want a ramp or wire style.
View K Tool International Universal Spark Plug Gap Gauge Tool KTI73701 on Amazon
Care and Setup
- Look up the gap figure for your engine in its own manual before you measure.
- Wipe oil and dirt from the electrodes and the gauge first.
- Bend the side electrode only a little at a time, and never press on the center electrode.
- Keep gauges dry and out of a loose drawer so the edges stay clean.
Mistakes to Avoid
- Trusting a printed scale without comparing it to a known good gauge.
- Prying on the center electrode instead of the side electrode.
- Assuming a pre-gapped plug is correct for your engine.
- Buying a wire set when your gap is outside its range.
Spark Plug Gap Tool FAQ
What is the difference between a coin gauge and a wire gauge?
A coin gauge has a tapered edge with a scale, so the gap is read where the plug electrode stops. A wire gauge uses a set of round wires of known sizes that you slide into the gap.
Which tool lists a metric scale?
The A and E 4450A shows one on the reverse side and the OEMTOOLS 25352 stamps metric sizes on the back.
The Short Version
For a coin with a stated range, the CTA 3235 or the K Tool. For a pocket clip, the A and E. For fixed wire sizes, the CTA 3238. For inch and metric, the OEMTOOLS. For a side wire adjuster, the Lisle.