M2x21 Viton O-Ring 75A, 21 mm ID 25 mm OD - Durable Metric Seal

In this review the M2x21 Viton O-Ring is evaluated for common sealing tasks where chemical resistance and temperature tolerance matter. The bottom line: this pack of 100 small black Viton rings is best for technicians and hobbyists who need reliable, repeatable seals for threaded barrels, carburetor seats, or hydraulic fittings; its single biggest strength is material choice, as the Viton fluorocarbon elastomer balances fuel and chemical resistance with wide temperature performance. For basic sealing and thread protection needs the rings offer strong value when buying in bulk.

Key Features

• Material: Made of Viton, the compound provides resistance to many fuels and chemicals, reducing premature swelling or degradation in compatible fluids.
• Temperature range: Rated for a wide operating range, these O-rings remain functional in both subzero service and high-heat environments for many applications.
• Hardness: The 75A durometer gives a mid-range firmness that seals well between cylindrical overlapping surfaces without being too stiff to compress.
• Form factor: The round cross-section creates a consistent sealing surface that works well in static and low-movement couplings.
• Pack quantity: Supplied as a pack of 100, making it economical for maintenance shops and projects requiring repeated replacements.

Who It's For

The O-ring is aimed at maintenance technicians, modelers, automotive DIYers and equipment owners who need a small, chemical-resistant seal for threaded barrels, carburetor seats, hydraulic connections or protective thread covers. Its size and hardness make it a practical choice for applications that require durability across a wide temperature span.

Those working with strong acids, concentrated alkalis, ammonia gas, certain amines or glycol-based brake fluids should look for alternative elastomers, since Viton is vulnerable to those specific chemicals. If extremely soft sealing material is required, a lower durometer compound would be more appropriate.

Pros & Cons

Pros

• Good chemical and fuel resistance for compatible fluids, making it suitable around many aromatic and aliphatic hydrocarbons.
• Wide usable temperature range that supports both cold and high-heat service.
• Bulk pack of 100 offers strong value and ready stock for recurring maintenance.
• Customers report reliable fit and seal quality for common threaded barrels and carburetor seats.

Cons

• Not compatible with low molecular weight organic acids, ammonia, some alkalis and glycol-based brake fluids, limiting use in those environments.

Specifications

Material	Viton (fluorocarbon elastomer)
Durometer	75A
Cross-section	Round
Inner diameter (ID)	21 mm
Outer diameter (OD)	25 mm
Width	2 mm
Pack quantity	100 pieces

Our Verdict

The M2x21 Viton O-Ring is a practical, cost-effective choice for anyone needing small metric seals that resist fuels and many chemicals while tolerating wide temperatures. Buy this pack if you want dependable thread protection, carburetor seat seals or general-purpose maintenance stock, but choose a different elastomer where exposure to ammonia, strong alkalis or glycol brake fluids is expected.

Frequently Asked Questions

Are these O-rings suitable for fuel systems?
Yes, they are compatible with many non-flammable hydraulic fuels and common hydrocarbons, but avoid use with incompatible fluids listed in the product notes.

What temperature range will they handle?
They are usable across a wide temperature span from low subzero conditions to high heat as specified for Viton materials.

Will they fit threaded barrels and carburetor seats?
Customers report good fit and seal quality on several threaded barrels and small carburetor seat applications due to the 21 mm ID and 75A hardness.