Have a 2012 troybuilt riding mower with a 17.5 hp engine. what spark plug does it take?

you need model # of mower and type of engine, ie: Kohler, Braggs, Honda, etc

Does this replace rc12yc?

No the thread portion is to long

Will this fit a john deer js40 self propelled walk behind mower?

Yes, I think the B&S 491055S will fit the John Deere JS40 mower. The John Deere part number for the JS40 spark plug is M78543 (JD Model JS40 maintenance sheet). I found 4 replacement plugs for the M78543 spark plug from a cross-reference website: Brisk 1326, Brisk DR17YC, Champion 71, and Champion RC12YC. It is important to measure the length of the threads on the original spark plug and compare it to the new or replacement plug. If the threads are too long you run the risk of the piston impacting the bottom of the spark plug; ruining your engine. I've used the Champion RC12YC on my JD E100 riding mower that has a B&S engine with the B&S 491055S spark plug. The Champion RC12YC is one of the replacement spark plugs for the 491055S.

Are these spark plugs b&s plugs or off brand plugs? thank you be safe out there

Hi they are briggs and Stratton brand.

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491055-2pk Spark Plug (2 Pack) Replaces 805015/72347/491055/Champion RC12Y

Product ID: 13521976

Details

Brand
Briggs &
Core Material
Copper
Thread Size
491055
Top Material Type
Metal
Vehicle Service Type
Lawn Mower

⚡Copper core for superior conductivity

🌿Optimized for lawn mower engines

🔧OEM precision fit for seamless installation

$16.73

Duties & taxes included

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Description

⚡ Ignite your mower’s potential—because your lawn deserves the best!

DOUBLE THE VALUE - Two-pack bulk packaging means you’re always ready for maintenance without extra trips.
TRUSTED BY THOUSANDS - Rated 4.7 stars by nearly 3,000 users who demand reliability and longevity.
PLUG PLAY PRECISION - Genuine OEM replacement ensures perfect compatibility with Briggs & Stratton and Kohler engines—no guesswork needed.
POWER YOUR LAWN LIKE A PRO - Copper core spark plugs deliver consistent, high-performance ignition every time.
KEEP YOUR GREEN SPACE PRISTINE - Specifically engineered for lawn mowers, these plugs maximize engine efficiency and reduce downtime.

The Briggs & Stratton 491055-2pk Spark Plug set includes two genuine OEM spark plugs designed for optimal performance in lawn mower engines. Featuring a copper core for enhanced conductivity and precision fit for a wide range of Briggs & Stratton and Kohler models, these plugs ensure reliable ignition and engine efficiency. Highly rated by thousands of users, this two-pack offers great value and peace of mind for professional-grade lawn care.

Specifications

ASIN	B00GG1BVOQ
Automotive Fit Type	Vehicle Specific Fit
Best Sellers Rank	#2,817 in Patio, Lawn & Garden ( See Top 100 in Patio, Lawn & Garden ) #3 in Lawn Mower Spark Plugs
Brand Name	Briggs & Stratton
Compatible with Vehicle Type	Lawn Mower
Core Material	Copper
Customer Reviews	4.7 4.7 out of 5 stars (2,969)
Item Weight	3.04 ounces
Manufacturer	Briggs and Stratton
Manufacturer Part Number	491055
Model Number	491055S
OEM Equivalent Part Number	491055
Thread Size	491055
Top Material Type	Metal
UPC	704660036378
Unit Count	2 Count

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