• 521237 Air Filter Assembly – Royal Enfield Thunderbird 350 OEM
  • 521237 Air Filter Assembly – Thunderbird 350 UCE (OEM)
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UNDER THE HOOD

Royal Enfield 521237 – Air Filter Assembly for Thunderbird 350 (UCE – TBTS BS3 & BS4/ABS “NTB 350”) – Genuine OEM

Royal Enfield 521237 – Air Filter Assembly for Thunderbird 350 (UCE – TBTS BS3 & BS4/ABS “NTB 350”) – Genuine OEM

Rs. 598.00
Rs. 619.00 Rs. 598.00
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Important Order Policy
Please order only after confirming the part number, model, variant, year, side, connector type and compatibility. All orders are non-cancellable once placed. Correctly shipped spare parts are not eligible for return, exchange or refund due to wrong selection, wrong diagnosis, fitment mismatch, mechanic recommendation or change of mind. Electrical/electronic items are additionally non-returnable once opened, installed, plugged in, tested or used. Wrong item, damaged item or missing item claims require a complete unboxing video within 24 hours. Read full Return & Warranty Policy

Restore factory breathing and protect your engine with the genuine Royal Enfield 521237 – Air Filter Assembly. This is the complete OE air cleaner unit for the Thunderbird 350 UCE platform—listed by dealers specifically for TBTS (BS3) and BS4/ABS Thunderbird 350 (often shown as “NTB 350” in parts listings). Because it’s OEM, the housing, sealing lip, mounting points and filter media match the original, ensuring dust-tight sealing, correct intake noise, and plug-and-play fit on the stock airbox bracket—no drilling or adjustments.

If your bike shows reduced mileage, dull throttle response, or intake howl after a fall or deep clean, a deformed/dirty filter housing can be the culprit. Swapping to the 521237 Air Filter Assy restores the designed flow and filtration level. We’ve verified the part name and application across multiple sources that list “AIR FILTER ASSY – 521237” for Thunderbird 350 (TBTS / NTB 350) and as a Royal Enfield genuine part. Only the confirmed models below are included to keep returns near zero.

Key Features

  • Genuine OEM Royal Enfield Air Filter Assembly – 521237. 

  • Direct replacement for Thunderbird 350 UCE air cleaner unit (complete). 

  • Correct OE sealing & mounting geometry for dust-tight fit.

  • Factory-spec filtration media for engine protection & mileage.

  • Restores stock intake sound and airflow—no tuning required.

  • Ships in OE packaging; authenticity guaranteed.

Compatibility Table 

Model Engine / Platform BS Stage / Years Notes
Thunderbird 350 (TBTS) 346cc UCE BS3 (≈2009–2012) Listed explicitly for TBTS. 
Thunderbird 350 (BS4/ABS) (“NTB 350” in listings) 346cc UCE BS4 (≈2017–2020) Dealers show 521237 for BS4 ABS T’bird 350. 

CHECK PART NUMBER BEFORE PURCHASE

Variants

  • N/A for LH/RH. If you need only the filter element, order the element PN specific to your variant; this listing is the assembly.

FAQs

Q1. Is this the full air filter box or just the paper element?
This listing is the Air Filter Assembly (OE housing with filter as supplied by RE for the Thunderbird 350).

Q2. Will 521237 fit my Thunderbird 350 ABS (BS4)?
Yes—dealers list 521237 for Thunderbird 350 ABS/BS4 (often labelled NTB 350). =

Q3. Does it need tuning after replacement?
No. It’s OEM; install and ride. Check idle after replacement and ensure the snorkel and clamps are seated.

Q4. How often should I replace it?
Inspect every service; replace per your RE schedule or sooner in dusty conditions.

Verify Fitment on Official Brand Portals

For selected genuine spare parts, you can cross-check the part number on the official brand portals before ordering.

Royal Enfield Official Spares Portal

Hero MotoCorp Official eCatalogue

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