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Which lawn mower spark plug matches the engine

Updated: October 2026

You have the old plug in your hand and a tab of 14 mm listings that all say lawnmower. Which lawn mower spark plug to buy is the code on that plug, or the code in the engine manual, not the word in the title. Briggs & Stratton UK warns that a plug can screw in and still cause running problems and possible internal damage. The [spark plug lawnmower comparison](/hub/lawn-and-garden-equipment/spark-plug-lawnmower) holds the twelve amazon.co.uk listings, with saved shelf prices from about £3.54 to about £8.89. Peter F. used those saved listings and public UK charts on 22 October 2026. There was no lab test. A qualifying purchase can earn a commission at no extra cost to you.

You have the old plug in your hand and a tab of 14 mm listings that all say lawnmower. Which lawn mower spark plug to buy is the code on that plug, or the code in the engine manual, not the word in the title.

Our top picks

Briggs & Stratton Briggs & Stratton RC12YC pair

Best overall

Briggs & Stratton Briggs & Stratton RC12YC pair
9.6/10about £7.99
View offer
NGK NGK BPMR7A

Best value

NGK NGK BPMR7A
9.4/10about £3.91
View offer
UYUYong UYUYong RJ19LM, 3

Rank 3

UYUYong UYUYong RJ19LM, 3
8.6/10about £4.89
View offer
On this page
  1. 1.Read the old plug before you search
  2. 2.Three families, not one lawnmower plug
  3. 3.Reach, hex, resistor and heat range
  4. 4.What a cross-reference bullet cannot promise
  5. 5.Then choose a listing

Read the old plug before you search

The code is usually on the ceramic or the metal shell. Write it down before you wipe the plug, because a black nose hides the letters. If the porcelain is cracked or the electrodes are burnt past reading, use the engine model on the shroud and, for a Briggs Quantum, the code date. The Briggs UK chart changes the part and the gap around those dates. A title that says lawn mower spark plug does not replace that line. RJ19LM, RC12YC and BPMR7A are not three stock levels of one part.

Three families, not one lawnmower plug

Older Briggs walk-behinds in the Classic, Sprint and Quattro pattern often take a flathead plug, commonly RJ19LM or J19LM. Many larger Briggs engines are overhead valve and call for RC12YC, or part numbers on the UK chart such as 491055S and 692051. Quantum rows can be RJ19LMC or RJ2YLE, and some specify 0.020 in (0.51 mm) rather than 0.030 in (0.76 mm). Match the code date before you trust a title that lists Quantum among a dozen models. That split is on RJ19LM vs RC12YC. Short-reach plugs such as BPMR7A are a third family, with 9.5 mm of reach on the NGK page.
Briggs & Stratton Briggs & Stratton RC12YC pair

Testsieger

Briggs & Stratton Briggs & Stratton RC12YC pair
9.6/10about £7.99
View offer

Reach, hex, resistor and heat range

Several 14 mm plugs will start in the same hole. Reach is how far the thread goes into the chamber. NGK puts BPMR7A at 9.5 mm of reach. The F6RTC pair in this set states 14 mm by 19 mm of thread. Those reaches are not a choice of brand. The saved BPMR7A listing prints 9.5 mm in the gap cell and does not say whether that figure is the gap or the reach. Do not merge it with the NGK 0.7 mm gap. UK reviews of the RJ19LM three-pack say the nut will not take a 13/16 socket. The letter R means a resistor, and a 5 and a 6 in the BPR series are not the same plug.

What a cross-reference bullet cannot promise

A bullet that lists a hundred codes is a claim. The Adefol cross at about £4.74 lists BPMR7A, and its thread cell says M10. On the NGK page that code is a 14 mm part. One review says there is no resistor, while R-codes sit on the cross list. Check the plug that arrives against the one you removed. The Talinco two-pack at about £4.99 has no customer-reviews line, an L7T included line, and Classic, Sprint, Quattro and Quantum in the bullets. Do not treat those words as one fit. The BPR5ES file says iridium in the material cells and the type name does not. One UK review disputes the metal. Do not call it an iridium plug.

Then choose a listing

Once the code, the reach and the heat range agree, price is a fair comparison. Pack-count conflicts, and the two files with no review line, stay on the main comparison. Do not gap or tighten anything until the code matches. Removal and the Briggs tightening ceiling are on how to change a lawn mower spark plug.

Common questions

Which plug does a Briggs lawn mower take?
It depends on the engine, not on the brand of the mower deck. Flathead Classic, Sprint and Quattro pattern engines often take RJ19LM or J19LM. Many overhead-valve Briggs engines take RC12YC, or the part numbers on the Briggs UK chart for that row. Quantum engines need the code date, because the chart changes the part and the gap around those dates.
Can I use a chainsaw plug in a four-stroke mower?
Only if that mower’s manual or old plug is the same code. BPMR7A is a short-reach resistor plug that Husqvarna UK lists for brushcutters and chainsaws. A four-stroke walk-behind that calls for RJ19LM or RC12YC is a different reach and a different family. Shared words such as garden or lawnmower on a listing do not make the swap safe.
What does the R in the code mean?
R marks a resistor plug. NGK states about 10 kΩ on BPMR7A. A non-resistor code, such as the CJ8 one UK reviewer was replacing, is not the same part with the R left off. One review in the BPMR7A file said the resistor was a poor swap for that saw. If the old plug has no R, do not assume an R-code cross is an improvement.
Why did a 13/16 socket not fit an RJ19LM listing?
The UYUYong three-pack is sold as RJ19LM, and the file has no hex measurement of its own. Two UK reviews say the nut is smaller than a Champion equivalent and that a 13/16 socket does not fit. Champion-pattern flathead plugs are often that larger hex. Measure the nut you have, or take the socket to the plug, before you assume the listing copied the Champion size.
Does a car-plug rank mean it fits the mower?
No. Rank is Amazon’s list for that category, not a fit certificate. The BPR5ES listing is ranked in car spark plugs and still has UK mower reviews for engines that wanted that code. The Briggs RC12YC pair is also ranked in car spark plugs. Fit comes from the code on your engine. A missing review line is not a quality score.

Related pages

Lawn mower won't start spark plug

Best lawn mower spark plug

Spark plug lawnmower

How to change a lawn mower spark plug and set the gap

RJ19LM vs RC12YC spark plug codes for Briggs engines

Sources

Buying notes from the sources below, checked for this page on 22 October 2026. Prices, stars and review counts are from the amazon.co.uk captures of that date. Two listings had no customer-reviews line.

  1. Briggs & Stratton UK: identifying the correct spark plug and gap (retrieved 22 October 2026)
  2. Briggs & Stratton UK: servicing the spark plug (retrieved 22 October 2026)
  3. Briggs & Stratton UK: engine problem solving (retrieved 22 October 2026)
  4. NGK: BPMR7A nickel spark plug (retrieved 22 October 2026)
  5. Husqvarna UK: spark plug spare (retrieved 22 October 2026)
  6. Husqvarna UK: how to check a spark plug gap (retrieved 22 October 2026)
  7. HSE: staying safe with petrol (retrieved 22 October 2026)
  8. Consumer Rights Act 2015, section 9 (retrieved 22 October 2026)