{"product_id":"royal-enfield-521129-b-o-ring-thunderbird-350-500-bullet-500-electra-x-500","title":"Royal Enfield O Ring for Thunderbird 350, Thunderbird 500, Bullet 500 \u0026 Electra X 500 – 521129\/B","description":"\u003ch2\u003eRoyal Enfield O Ring for Thunderbird 350, Thunderbird 500, Bullet 500 \u0026amp; Electra X 500 – 521129\/B\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003e521129\/B\u003c\/strong\u003e is a genuine Royal Enfield \u003cstrong\u003eO RING\u003c\/strong\u003e. OEM-style Royal Enfield parts sources identify this exact part number as \u003cstrong\u003eO RING\u003c\/strong\u003e, and specialist Royal Enfield parts references also identify the same family as an \u003cstrong\u003eO-RING\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp\u003eThe strongest direct fitment evidence is centered on the older Thunderbird-family and related 500cc applications. Direct seller support explicitly links \u003cstrong\u003e521129\u003c\/strong\u003e to \u003cstrong\u003eTBTS\u003c\/strong\u003e and \u003cstrong\u003eNTB 350\u003c\/strong\u003e, while specialist partsbook pages also show the same O-ring family in \u003cstrong\u003eair filter \/ air filter assembly\u003c\/strong\u003e context for \u003cstrong\u003e500 Electra X\u003c\/strong\u003e and older 500 models.\u003c\/p\u003e\n\u003cp\u003eThis is a small sealing O-ring, not a decorative rubber part. Buyers may also search for it as \u003cstrong\u003eRoyal Enfield air filter O ring\u003c\/strong\u003e, \u003cstrong\u003eThunderbird O ring\u003c\/strong\u003e, \u003cstrong\u003eNTB 350 O ring\u003c\/strong\u003e, \u003cstrong\u003eBullet 500 O ring\u003c\/strong\u003e, and \u003cstrong\u003eElectra X airbox O ring\u003c\/strong\u003e. Because O-rings are easy to confuse with generic hardware, exact part-number matching matters more than appearance alone.\u003c\/p\u003e\n\n\u003ch3\u003eWhy Buyers Need It\u003c\/h3\u003e\n\u003cp\u003eThis type of part is usually replaced when the original sealing ring becomes hard, flattened, cracked, cut, or missing during service. Using the correct OEM O-ring helps maintain proper sealing in the assembly where it is used, instead of relying on a loose generic substitute.\u003c\/p\u003e\n\n\u003ch3\u003eKey Features\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eGenuine Royal Enfield OEM sealing part\u003c\/li\u003e\n\u003cli\u003ePart number: \u003cstrong\u003e521129\/B\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eOfficial description: \u003cstrong\u003eO RING\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eStrong direct seller fitment for \u003cstrong\u003eTBTS\u003c\/strong\u003e and \u003cstrong\u003eNTB 350\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli\u003eAlso appears in specialist \u003cstrong\u003eair filter \/ air filter assembly\u003c\/strong\u003e parts context for older 500-family applications\u003c\/li\u003e\n\u003cli\u003eSmall OEM sealing part where exact size and fit matter\u003c\/li\u003e\n\u003cli\u003eBetter buyer outcome than using a random local O-ring without exact matching\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eVerified Compatibility\u003c\/h3\u003e\n\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eModel\u003c\/th\u003e\n\u003cth\u003eStatus\u003c\/th\u003e\n\u003cth\u003eNotes\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eThunderbird 350 \/ TBTS\u003c\/td\u003e\n\u003ctd\u003eConfirmed\u003c\/td\u003e\n\u003ctd\u003eDirect seller support explicitly lists TBTS for 521129.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eThunderbird 350 \/ NTB 350\u003c\/td\u003e\n\u003ctd\u003eConfirmed\u003c\/td\u003e\n\u003ctd\u003eDirect seller support explicitly lists NTB 350 for 521129.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003e500 Electra X\u003c\/td\u003e\n\u003ctd\u003eSupported\u003c\/td\u003e\n\u003ctd\u003eSpecialist partsbook pages show 521129 as O-RING in the air filter family context.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBullet 500 \/ older 500 air-filter family context\u003c\/td\u003e\n\u003ctd\u003eSupported\u003c\/td\u003e\n\u003ctd\u003eSpecialist partsbook pages show 521129 as O-RING in older 500 airfilter assembly context.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eThunderbird 500\u003c\/td\u003e\n\u003ctd\u003eSupported\u003c\/td\u003e\n\u003ctd\u003eSupported from 500-family air-filter assembly context plus Thunderbird-family seller mapping.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOther Royal Enfield models\u003c\/td\u003e\n\u003ctd\u003eDo not assume\u003c\/td\u003e\n\u003ctd\u003eCurrent evidence does not justify broad all-model fitment claims.\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch3\u003eWhat’s in the Box\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003e1 x Genuine Royal Enfield O Ring – 521129\/B\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eBuyer-Focused Fitment Note\u003c\/h3\u003e\n\u003cp\u003ePlease order only after matching your old part number and application. This is a \u003cstrong\u003esmall sealing O-ring\u003c\/strong\u003e, and wrong orders are common when buyers assume any similar rubber ring will work. The safest dispatch basis is exact part-number confirmation plus old-part\/application match.\u003c\/p\u003e\n\n\u003ch3\u003eFAQs\u003c\/h3\u003e\n\u003cp\u003e\u003cstrong\u003e1. What is 521129\/B?\u003c\/strong\u003e\u003cbr\u003eIt is the genuine Royal Enfield \u003cstrong\u003eO RING\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e2. Which bikes can I safely buy this for?\u003c\/strong\u003e\u003cbr\u003eThe strongest direct proof is for \u003cstrong\u003eTBTS\u003c\/strong\u003e and \u003cstrong\u003eNTB 350\u003c\/strong\u003e. There is also supporting parts context for older \u003cstrong\u003e500 Electra X\u003c\/strong\u003e and older 500 air-filter assembly applications.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e3. Is it OEM?\u003c\/strong\u003e\u003cbr\u003eYes. It is listed as a genuine Royal Enfield part by OEM-style and specialist Royal Enfield sources.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e4. Is this a generic rubber O-ring?\u003c\/strong\u003e\u003cbr\u003eNo. It should be treated as a model\/application-specific OEM sealing part, not a random universal ring.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e5. Where is it used?\u003c\/strong\u003e\u003cbr\u003eThe clearest specialist partsbook evidence places it in \u003cstrong\u003eair filter \/ air filter assembly\u003c\/strong\u003e context on older Royal Enfield pages.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e6. Can I fit it on any Royal Enfield if it looks similar?\u003c\/strong\u003e\u003cbr\u003eNo. Current evidence supports specific older Thunderbird and older 500\/Electra-family applications only.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e7. What should I check before ordering?\u003c\/strong\u003e\u003cbr\u003eCheck your motorcycle model, old O-ring application, and exact part number \u003cstrong\u003e521129\/B\u003c\/strong\u003e.\u003c\/p\u003e","brand":"Royal Enfield","offers":[{"title":"Default Title","offer_id":51390545690919,"sku":"521129\/B","price":50.0,"currency_code":"INR","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0878\/7447\/0183\/files\/E8365CCE-5876-4A75-9E36-9E331504570C.jpg?v=1778942079","url":"https:\/\/underthehood.co.in\/products\/royal-enfield-521129-b-o-ring-thunderbird-350-500-bullet-500-electra-x-500","provider":"UNDER THE HOOD","version":"1.0","type":"link"}