{"product_id":"st200-spark-plug-tester","title":"ST200 Dual Spark Plug Tester with Magnifier","description":"\u003cdiv class=\"obd-st200-description\"\u003e\n\u003cp\u003e\u003cstrong\u003eSee the spark clearly. Compare two plugs. Test with confidence.\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe \u003cstrong\u003eOBDResource ST200 Spark Plug Tester\u003c\/strong\u003e combines dual-plug comparison, magnified viewing, and adjustable firing frequency in one easy-to-use bench tool. Inspect removed spark plugs from compatible cars, motorcycles, lawn mowers, and other gasoline-powered equipment without running the engine.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCheck before purchasing:\u003c\/strong\u003e The maximum outside diameter of the spark plug’s \u003cstrong\u003eceramic insulator must be 13 mm or less\u003c\/strong\u003e. This limit applies to both test sockets. It does \u003cstrong\u003enot\u003c\/strong\u003e refer to the metal thread diameter or hex size. Please review the fitment guide below.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch2\u003eKey Features\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eDual Spark Plug Comparison\u003c\/strong\u003e\u003cbr\u003eTest two compatible spark plugs simultaneously. Place a suspect plug alongside a known-good plug of the same specification to compare firing consistency under the same test setting.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eMagnified Viewing for Easier Inspection\u003c\/strong\u003e\u003cbr\u003eBuilt-in magnifying windows in the protective cover bring the electrode area into closer view, making spark activity easier to observe. Keep the cover installed throughout testing.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdjustable 0–6,000 Simulated RPM\u003c\/strong\u003e\u003cbr\u003eUse the rotary knob to adjust firing frequency and observe spark behavior at different settings. The RPM scale represents a simulated test setting, not a measurement of actual engine speed.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eFlexible Fitment for Short and Long Spark Plugs\u003c\/strong\u003e\u003cbr\u003eSpring-loaded test sockets and included spacers accommodate a variety of compatible plug bodies. Longer ceramic insulators may require one or two supplied spacers for correct positioning.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eSimple Controls and Clear Status Indicators\u003c\/strong\u003e\u003cbr\u003eA rotary control, main indicator, and two high-voltage indicators make operation straightforward. Indicator lights show operating status; they do not provide an automatic good-or-bad verdict.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e100–240V AC Adapter Input\u003c\/strong\u003e\u003cbr\u003ePower the tester using the supplied adapter and a compatible AC outlet. Test removed spark plugs on the workbench without connecting the tester to a vehicle battery.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch2\u003eCheck Compatibility Before You Buy\u003c\/h2\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cstrong\u003eMeasure the ceramic diameter.\u003c\/strong\u003e Use a caliper to measure the widest part of the ceramic insulator, including any raised ribs. The largest reading must be \u003cstrong\u003e13 mm or less\u003c\/strong\u003e.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompare the remaining dimensions.\u003c\/strong\u003e Check your existing spark plug against the tested samples below. Brand name or thread size alone does not confirm fitment.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCheck the exposed ceramic length.\u003c\/strong\u003e If it is longer than the F7TC reference sample or exceeds \u003cstrong\u003e35 mm\u003c\/strong\u003e, use one or two included spacers as needed.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eConfirm proper seating.\u003c\/strong\u003e The plug must seat securely, maintain electrical contact, and allow the protective cover to fit correctly. Never force a plug into the test socket.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003cp\u003e\u003cstrong\u003eCompatibility is based on dimensions, not brand.\u003c\/strong\u003e Spark plugs from any brand that match the listed compatible dimensions can be tested, provided the ceramic diameter, seating, and cover clearance meet the requirements. Measure your existing spark plug before purchasing.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eImportant:\u003c\/strong\u003e A ceramic diameter greater than 13 mm is incompatible. Adding spacers does not increase the test socket diameter.\u003c\/p\u003e\n\u003ch3\u003eTested Spark Plug Compatibility\u003c\/h3\u003e\n\u003cp\u003eThese nine samples have passed OBDResource ST200 fitment and testing. They are listed in the same left-to-right order as the reference lineup.\u003c\/p\u003e\n\u003cdiv role=\"region\" style=\"max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch;\" tabindex=\"0\"\u003e\n\u003ctable style=\"width: 98.7216%; border-collapse: collapse;\" height=\"312\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth scope=\"col\" style=\"width: 4.17311%;\"\u003eNo.\u003c\/th\u003e\n\u003cth scope=\"col\" style=\"width: 22.102%;\"\u003eBrand \/ Model\u003c\/th\u003e\n\u003cth scope=\"col\" style=\"width: 9.73725%;\"\u003eThread\u003c\/th\u003e\n\u003cth scope=\"col\" style=\"width: 14.374%;\"\u003eReach\u003c\/th\u003e\n\u003cth scope=\"col\" style=\"width: 20.5564%;\"\u003eHex Size\u003c\/th\u003e\n\u003cth scope=\"col\" style=\"width: 29.2117%;\"\u003eElectrode \/ Type\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e1\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eF7TC — brand unconfirmed\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM14 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e19 mm\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e20.8 mm\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eThree ground electrodes\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e2\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eGL F7TC\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM14 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e19 mm\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e20.8 mm\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eSingle ground electrode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e3\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eDENSO SC20HR11\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM12 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e26.5 mm\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e14 mm\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eIridium; single ground electrode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e4\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eE3 E3.36\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM12 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e19.05 mm (3\/4 in)\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e5\/8 in (approx. 16 mm)\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eDiamondFIRE; fixed gap\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e5\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eAutolite 4194\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM10 × 1.0\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e12.7 mm (1\/2 in)\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e5\/8 in (approx. 16 mm)\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eCopper core; single ground electrode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e6\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eCHAMPION RJ19LM\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM14 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e9.5 mm (3\/8 in)\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e13\/16 in (approx. 20.6 mm)\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eResistor; single ground electrode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e7\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eAutolite 458\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM14 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e9.5 mm (3\/8 in)\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e13\/16 in (approx. 20.6 mm)\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eCopper core; single ground electrode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e8\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eAutolite 254\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM14 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003e9.5 mm (3\/8 in)\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e3\/4 in (approx. 19 mm)\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eCopper core; single ground electrode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 4.17311%;\"\u003e9\u003c\/td\u003e\n\u003ctd style=\"width: 22.102%;\"\u003eCHAMPION DJ8J\u003c\/td\u003e\n\u003ctd style=\"width: 9.73725%;\"\u003eM14 × 1.25\u003c\/td\u003e\n\u003ctd style=\"width: 14.374%;\"\u003eApprox. 7.8 mm*\u003c\/td\u003e\n\u003ctd style=\"width: 20.5564%;\"\u003e5\/8 in (approx. 16 mm)\u003c\/td\u003e\n\u003ctd style=\"width: 29.2117%;\"\u003eNon-resistor; tapered seat\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/div\u003e\n\u003cp\u003e\u003csmall\u003e*DJ8J reach is recorded as 0.307 in (approximately 7.8 mm) from the DJ-series specification; some listings state 8.3 mm. Verify the physical measurement when using this model for dimensional comparison. The tested DJ8J sample fits the ST200. Inch-to-millimeter conversions are approximate. \u003c\/small\u003e\u003c\/p\u003e\n\u003cp\u003e\u003csmall\u003e This table identifies tested examples, not every compatible spark plug. Matching thread size alone does not establish compatibility. Always check the maximum ceramic diameter and correct seating. \u003c\/small\u003e\u003c\/p\u003e\n\u003chr\u003e\n\u003ch2\u003eHow to Use the ST200\u003c\/h2\u003e\n\u003col\u003e\n\u003cli\u003e\n\u003cstrong\u003ePrepare the tester.\u003c\/strong\u003e Switch it off and disconnect power. Use clean, dry spark plugs and work away from fuel and flammable vapors.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003ePosition the spark plugs.\u003c\/strong\u003e Fit compatible plugs into the test sockets. For comparison, use a known-good plug of the same specification as the suspect plug.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAdd spacers when needed.\u003c\/strong\u003e If the exposed ceramic section is longer than the F7TC reference sample or exceeds 35 mm, place one or two included spacers inside the ring-shaped insert, then insert the spark plug. Use the number needed for proper seating, electrical contact, and cover clearance.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eInstall the protective cover.\u003c\/strong\u003e Check that it fits correctly before connecting the supplied adapter and switching on the tester.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eAdjust and observe.\u003c\/strong\u003e Turn the rotary knob to vary the firing frequency. Observe spark consistency through the magnifying windows.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eSwitch off before handling.\u003c\/strong\u003e Disconnect power before removing, swapping, or repositioning either spark plug.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003cp\u003e\u003cstrong\u003eUnderstanding the result:\u003c\/strong\u003e The ST200 provides a visual bench test. It does not reproduce cylinder pressure, combustion temperature, or engine load. A plug that sparks on the bench may still fail in the engine. Use the result alongside the engine manufacturer’s diagnostic procedures.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch2\u003eTypical Applications\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eCompare a suspect spark plug with a known-good reference plug.\u003c\/li\u003e\n\u003cli\u003eObserve intermittent firing or absence of spark during bench testing.\u003c\/li\u003e\n\u003cli\u003eInspect firing behavior after spark plug cleaning or maintenance.\u003c\/li\u003e\n\u003cli\u003eSupport spark plug checks during hard-start or rough-running diagnosis.\u003c\/li\u003e\n\u003cli\u003eTest dimensionally compatible plugs used in cars, motorcycles, ATVs, lawn mowers, generators, and other gasoline-powered equipment.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr\u003e\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eModel:\u003c\/strong\u003e ST200\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTesting Capacity:\u003c\/strong\u003e Two spark plugs simultaneously\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eControl:\u003c\/strong\u003e Rotary firing-frequency adjustment\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eSimulated Speed Range:\u003c\/strong\u003e 0–6,000 RPM\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaximum Ceramic Outside Diameter:\u003c\/strong\u003e 13 mm per test socket\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eViewing:\u003c\/strong\u003e Protective cover with magnifying windows\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eFitment Adjustment:\u003c\/strong\u003e Spring-loaded sockets and included spacers\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003ePower Adapter Input:\u003c\/strong\u003e 100–240V AC\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eIndicators:\u003c\/strong\u003e Main indicator and two high-voltage indicators\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eApplication:\u003c\/strong\u003e Removed, dimensionally compatible gasoline-engine spark plugs\u003c\/p\u003e\n\u003chr\u003e\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003ch3\u003eHow do I check whether my spark plug fits before purchasing?\u003c\/h3\u003e\n\u003cp\u003eMeasure the maximum outside diameter of the ceramic insulator. It must be 13 mm or less. Then compare the remaining dimensions with the compatibility table and check whether spacers are needed for the exposed ceramic length.\u003c\/p\u003e\n\u003ch3\u003eWhich part does the 13 mm limit apply to?\u003c\/h3\u003e\n\u003cp\u003eIt applies to the ceramic insulator—the usually white section with the model number printed on it. Include raised ribs and measure the widest point. This limit does not refer to the metal threads or the hex used by a socket wrench.\u003c\/p\u003e\n\u003ch3\u003eHow should I measure the ceramic diameter?\u003c\/h3\u003e\n\u003cp\u003eUse a vernier or digital caliper. Gently measure across several locations, including the smooth section and raised ribs. Record the largest reading, not just a measurement taken in a narrower groove.\u003c\/p\u003e\n\u003ch3\u003eWill a ceramic diameter of exactly 13 mm fit?\u003c\/h3\u003e\n\u003cp\u003e13 mm is the maximum supported diameter. Recheck measurements near the limit and confirm the other fitment requirements. Do not round a larger reading down: 13.2 mm, for example, exceeds the limit. Never force the plug into the socket.\u003c\/p\u003e\n\u003ch3\u003eWhat does M14 mean? Can an M14 spark plug fit?\u003c\/h3\u003e\n\u003cp\u003eM14 identifies a metric thread with a nominal outside diameter of 14 mm. It describes the lower metal threaded section, while the ST200’s 13 mm limit applies to the upper ceramic section. An M14 spark plug can fit when its ceramic diameter and other dimensions meet the requirements.\u003c\/p\u003e\n\u003ch3\u003eWhat do thread pitch, reach, and hex size mean?\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eM14 × 1.25:\u003c\/strong\u003e A nominal thread diameter of 14 mm and a thread pitch of 1.25 mm. Pitch is the distance between adjacent thread crests, measured along the plug’s axis.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eReach:\u003c\/strong\u003e The axial distance from the specified mounting-seat reference to the end of the threaded shell, excluding the protruding firing electrodes. Follow the plug manufacturer’s measurement diagram, particularly for tapered-seat designs.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eHex Size:\u003c\/strong\u003e The distance across two opposite flat faces of the metal hex, used to select the correct socket wrench. It is not measured across the corners.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCeramic Insulator Length:\u003c\/strong\u003e The exposed upper ceramic section measured along the plug’s axis, excluding the top metal terminal and lower metal shell. It is not the overall spark plug length.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eCan I test a ceramic insulator longer than 35 mm?\u003c\/h3\u003e\n\u003cp\u003eA longer ceramic insulator does not automatically make the plug incompatible. If it is longer than the F7TC reference sample or exceeds 35 mm, use one or two included spacers as needed. Place them inside the ring-shaped insert before inserting the plug. Correct seating, electrical contact, and protective-cover clearance must be maintained.\u003c\/p\u003e\n\u003ch3\u003eCan spacers make a ceramic diameter greater than 13 mm fit?\u003c\/h3\u003e\n\u003cp\u003eNo. Spacers adjust seating height; they do not enlarge the test socket. A ceramic diameter greater than 13 mm remains incompatible.\u003c\/p\u003e\n\u003ch3\u003eCan I test brands or models that are not listed?\u003c\/h3\u003e\n\u003cp\u003eYes, if their relevant dimensions match the compatible specifications and they seat correctly. The table shows tested examples. Compatibility is not limited to those brands, but brand name, similar appearance, or an M14 marking alone does not confirm fitment.\u003c\/p\u003e\n\u003ch3\u003eDoes the ST200 test ignition coils or diesel glow plugs?\u003c\/h3\u003e\n\u003cp\u003eThe ST200 is designed for removed gasoline-engine spark plugs. It is not a vehicle ignition-coil tester or a diesel glow-plug tester.\u003c\/p\u003e\n\u003ch3\u003eWhat should I provide if I am unsure about compatibility?\u003c\/h3\u003e\n\u003cp\u003ePlease send the brand, complete model number, a photo of the entire spark plug, and caliper photos showing the maximum ceramic diameter and exposed ceramic length. \u003ca href=\"\/policies\/contact-information\"\u003eContact OBDResource support\u003c\/a\u003e before purchasing if you need help checking fitment.\u003c\/p\u003e\n\u003chr\u003e\n\u003ch2\u003eUse and Care\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eRead and follow the supplied instruction manual.\u003c\/li\u003e\n\u003cli\u003eKeep the protective cover installed during operation.\u003c\/li\u003e\n\u003cli\u003eNever touch spark plugs or test contacts while the tester is powered.\u003c\/li\u003e\n\u003cli\u003eDisconnect power before adjusting, inserting, or removing plugs.\u003c\/li\u003e\n\u003cli\u003eUse clean, dry plugs and keep the work area free of fuel vapors.\u003c\/li\u003e\n\u003cli\u003eKeep the tester dry and never force oversized plugs into the sockets.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/div\u003e","brand":"OBDResource","offers":[{"title":"Default Title","offer_id":45556260339778,"sku":"CC0501","price":49.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0658\/0414\/0610\/files\/OBDResource_ST200_Spark_Tester.jpg?v=1791929482","url":"https:\/\/obdresource.net\/products\/st200-spark-plug-tester","provider":"OBDResource USA","version":"1.0","type":"link"}