CTA Tools 3235 Spark Plug Gapper

Why I keep this spark plug gapper in my pocket

In my shop, a small, coin-style spark plug gapper lives on my keyring and gets used far more often than you’d think. The CTA gapper is the one I’ve been reaching for lately, and it’s reminded me why this simple tool still belongs in a modern toolkit. Spark plug gap matters—whether you’re chasing a misfire, setting up a fresh set of plugs, or just double-checking a tune. The CTA version hits the sweet spot: compact, sturdy, readable, and quick to use.

Build and design

The CTA gapper is the classic coin format: a circular ramp etched with both inch and metric graduations, plus an integrated slot to tweak the ground strap. It’s a one-piece, heavy-gauge metal tool that feels dense in the hand without being bulky. The finish resists pocket rash and shop grime, and the etched markings are filled for contrast, so you can read the numbers without hunting for good light.

There’s a small hole for a lanyard or keyring, which sounds like a throwaway feature until you realize how often a gapper goes missing in a drawer. The overall size is “right”—big enough to grip, small enough to live in a pocket.

CTA markets this line as professional grade, and in hand it feels that way. Edges are clean, the ramp transitions smoothly, and the bending notch has a crisp profile that doesn’t mar the ground strap when used correctly.

Accuracy and how it performs

Coin-style gappers are all about speed and consistency, and this one does both. I checked common targets—0.028, 0.032, 0.040, and 1.0 mm—against a set of feeler gauges. In the mid-range most plugs actually use (0.028–0.044 in), the CTA gapper tracked dead-on or within a hair’s breadth—well inside the tolerance you’ll get once the plug is torqued and heat-cycled. At the outer ends of the scale, especially above 1.0 mm, I noticed the usual coin-gauge caveat: you can be a touch off if you rely solely on the ramp. That’s not unique to this tool; it’s inherent to the format.

Here’s the workflow I recommend, and the one I use with this gapper:
- Measure where the plug is at by sliding the ramp into the gap until it stops and reading the marking at the contact point.
- Adjust using the built-in notch or the ramp itself—small, incremental tweaks.
- Re-check on the ramp.
- Verify final with a feeler gauge or a dedicated wire gauge if you’re chasing absolute precision.

Using the notch rather than prying hard with the ramp helps keep the ground strap straight and square to the center electrode.

Ergonomics and readability

Two things set this particular gapper apart. First, the ramp is truly smooth. Some disc gappers feel grabby and can “step” over the ground strap, which doesn’t inspire confidence. This one inserts and slides predictably, so you know you’re reading the gap rather than fighting friction.

Second, the legibility is excellent. The etchings are dark and crisp. In a dim bay or underhood shadow, I didn’t have to squint or tilt the tool to catch light. It sounds minor, but when you’re gapping a set of six or eight plugs, readable markings reduce mistakes and speed things up.

Durability in shop use

This isn’t a delicate precision instrument; it’s a rugged little disc that takes abuse. Mine’s already been knocked off a fender, rattled around with keys, and wiped down with brake cleaner more than once. No warping, no flaking, no rounding of the bending slot. The ramp edge stays true, which matters for repeatable readings. I wouldn’t call it indestructible—nothing is—but it’s a clear step above the flimsy stamped pieces you find at checkout counters.

Where it shines—and where it doesn’t

Strengths:
- Fast, repeatable setup across common gap ranges for modern plugs.
- Easy-to-read, dual-scale markings make it practical in real-world lighting.
- Sturdy enough to live on a keyring without bending out of spec.
- The notch offers controlled, clean adjustments with minimal risk of deforming the strap.

Limitations:
- Like all coin gappers, it’s not a metrology tool. If you need exactness to the last thousandth, verify with feeler gauges or a wire set.
- Fine-wire iridium and platinum plugs can be delicate; you should always adjust by bending only the ground strap and never touch the center electrode. The disc is safe to use, but heavy-handed adjustments can still misalign the strap.
- If you’re targeting unusually large or very tight gaps, the tool is still usable, but the verification step becomes more important.

Practical tips from the bench

• Aim small: Make tiny adjustments and re-check often. Big single moves are what bend straps off-center.
• Keep it square: After any adjustment, eyeball the ground strap’s alignment to the center electrode. If it’s off to one side, gently nudge it back using the notch.
• Verify the last step: A quick pass with a feeler gauge adds seconds and pays off with reliable ignition under load.
• Follow the spec: Trust the engine manufacturer’s gap spec, not the value printed on the plug box. Plugs ship with a generic gap that may not match your engine.

How it compares to other options

• Coin disc vs. feeler gauges: Feeler gauges are more precise for measuring, slower for adjusting. I like the disc for initial set and quick checks, then a feeler blade to confirm.
• Wire gauges: A wire set is excellent for measuring roundness of the gap and avoids wedging forces. Pairing the CTA disc for adjustments with a wire gauge for verification is a great combo.
• Cheap stamped discs: The CTA feels thicker, slides smoother, and has better legibility. The difference shows up most when you’re doing a full set of plugs or working at the edges of a spec range.

Fit and range for modern vehicles

Most late-model gasoline engines spec gaps in the 0.024–0.044 in range (0.6–1.1 mm). The CTA gapper covers that and more, with clearly marked increments. I’ve used it on compact electrode plugs for small turbo engines and larger traditional plugs alike. It’s also handy for quick checks on lawn equipment and small engines where “close enough” often solves a stubborn start.

Value

For a small spend, you get a tool that will likely outlast several cars in your driveway. The difference over bargain-bin discs isn’t just feel—it’s the consistency of readings and reduced tendency to scuff or deform the strap during adjustment. If you gap plugs a few times a year, that reliability is worth it. If you do it weekly, it’s a no-brainer.

The bottom line

The CTA gapper does exactly what a good gapper should: it measures and adjusts quickly, reads clearly, and stands up to shop use. It’s not trying to be a precision instrument, and it doesn’t need to be. Pair it with a feeler or wire gauge for your final check and you’ll have a reliable, repeatable process that protects plugs and delivers solid ignition performance.

Recommendation: I recommend this tool. It’s a durable, easy-to-read, coin-style gapper that makes quick work of spark plug setup and holds up to real-world use. It’s especially worth buying if you want something better than the flimsy alternatives and you appreciate accurate, repeatable results without fuss. Use it for the adjust-and-check steps, verify with a feeler gauge when precision matters, and you’ll be set for years.