MOTRIO spark plug (8550503321) fires the air-fuel charge with a precisely controlled spark at the correct electrode gap and heat range for your engine's combustion chamber geometry. Plug parameters — Thread Size: M12 x 1, 25, Spanner Size: 14 mm, Spark Plug: Bronze, Spark Plug: 54 — determine ignition timing accuracy, electrode longevity, and resistance to pre-ignition deposits across the full RPM range. Thread reach, seat type, and hex size are specified to fit ASTON MARTIN, LEXUS, MAZDA, SUBARU and 1 other makes cylinder heads without re-gapping or thread chasing. Replaces OE ignition references: 3444, 4711, 4912, 9091901253 and 4 more. MOTRIO ignition components are manufactured to SAE and DIN specifications and are approved for use in vehicles covered by manufacturer service agreements throughout Europe. Standard copper-core spark plugs last around 20,000–30,000 miles, while iridium or platinum-tipped plugs can last 60,000–100,000 miles — always follow the interval specified in your vehicle's service schedule. Symptoms of worn spark plugs include rough idling, engine misfires (often felt as a stumble under acceleration), increased fuel consumption, and difficulty starting in cold weather. Spark plug replacement is a straightforward DIY job on most engines — you need a spark plug socket, a torque wrench, and a gap gauge; allow 30–60 minutes for a four-cylinder engine, longer for boxer or V-configurations where access is tighter. Always match the heat range and electrode material specified by your engine manufacturer — fitting a plug with the wrong heat range can cause pre-ignition, fouling, or catalytic converter damage. Replacing spark plugs on schedule maintains optimal combustion efficiency, reduces harmful emissions, and prevents unburnt fuel from damaging the catalytic converter — a component that costs many times more to replace. Every part is dispatched with tracked delivery and a 14-day money-back guarantee with hassle-free returns.