Rubber and Plastic Sealing Products – Lecture 1: Standard Seals

1. Quick Overview

"Standard seals" actually follow two simple systems at the same time in international brand catalogs.

One system sorts them by shape and cross-section: O-ring, encapsulated O-ring, square ring, D-ring, X-ring (Quad-ring), and combined sealing washers.

The other system sorts them by how they are installed and the job they do: static seals, face seals, flange seals, and fastener seals.

Trelleborg, Freudenberg, Parker, and Hutchinson all organize their catalogs this way. They put O-rings, X-rings, flange seals, and combined washers together under one big "static seals" group instead of selling each one separately.

When you look at world-class brands, the ones worth studying for this category are: Trelleborg, Freudenberg Sealing Technologies, Parker Hannifin/Prädifa, and Hutchinson. For factory equipment, SKF is a good benchmark. In Asia, NOK is the standard to watch.

These companies do not just sell one rubber ring. They offer a complete package: materials, size standards, groove designs, application data, certifications, and sales channels.

2. How the Big International Brands Line Up

Trelleborg: Very complete static seal range. They openly list O-rings, FEP encapsulated O-rings, Quad-Ring/X-Ring, Bonded Seals (metal + rubber), Kantseal square rings, etc. Their style is "standard parts plus engineered static seal shapes."

Freudenberg Sealing Technologies: Strong in materials and full product families. They cover O-rings, X-rings, encapsulated O-rings, flange seals, and USIT-Rings for fasteners. They turn static seals into organized product groups.

Parker / Prädifa: They list O-rings, X-rings, D-rings, flange seals, fastener seals, and ORFS face seals. Their strong point is how tightly they link static seals with hydraulic and fluid connections.

Hutchinson: Covers O-rings, X-rings, Bonded Seals, and PFS flange seals. Their flange and Bonded Seal lines are very clear – good for matching European industrial static seal thinking.

SKF: In factory equipment, they offer O-rings, backup rings, square rings, and static seals. A solid benchmark for industrial matching.

NOK: O-rings and sealing solutions are their basic business. They cover cars, construction machines, semiconductors, hydrogen systems, and more. Good benchmark for Asian mass production and industry supply.

3. Product List – One by One

1. O-Ring Series

O-Ring

This is the foundation of all standard seals. Parker supplies them to AS 568B, DIN ISO 3601, JIS, and other standards. Freudenberg treats the O-ring as the classic static seal and also makes special dynamic versions. SKF and NOK do the same. When comparing with big brands, the real difference is not "can you make an O-ring?" but materials, stock of standard sizes, certifications, cleanliness, and delivery speed.

Encapsulated O-Ring

This is a higher-value product. Trelleborg's FEP O-ring uses a silicone or fluoro-rubber core with a seamless FEP outer layer. It gives excellent chemical resistance and low friction and meets ISO 3601, AS 568, BS 4518, etc. Freudenberg positions encapsulated O-rings for high-demand static seals and clearly states FEP/PFA versions are mainly for static use. Good for strong chemicals, corrosion, high-cleanliness, or food-contact jobs. Volume may not be huge, but the brand value is higher.

Square Ring

International brands usually call it square ring or square-section ring. Trelleborg's Kantseal is the classic example: square cross-section, mainly for static seals on SAE flanges and end covers. SKF also puts square rings under static seals. Its value comes from fitting flange and cover designs better than a simple round O-ring.

D-Ring

Parker's definition is clear: it is an economical replacement for traditional radial seals and works in static, reciprocating, or oscillating applications. The flat bottom helps stop spiral twist failure. Freudenberg also offers D-rings as a special O-ring shape. Not a high-volume item, but it adds real value where assembly stability matters.

X-Ring / Quad-Ring

The most typical upgrade from a normal O-ring. Trelleborg's Quad-Ring/X-Ring has four lips, works both ways, and can be used static or dynamic. It gives better sealing and lower friction than a standard O-ring. Freudenberg's X-Ring XR covers flanges, end covers, pipe fittings, and reciprocating/rotating jobs. X-rings are a great way to move from standard parts to branded upgrade parts.

Rubber Gaskets / Flat Gaskets

In international catalogs these are not sold as "star standard items." They fall under gaskets / flange gaskets / flat flange seals. Freudenberg treats gaskets as part of the sealing system. Trelleborg offers standard flange gaskets for process industry. James Walker focuses on flat flange sealing materials. In other words, these are more "drawing-specific" or "job-specific" parts. Brand strength comes from material and application know-how rather than the shape alone.

2. Groove and Fitting Seals

Static Seals

This is not one single shape. It is the name for all seals with no relative movement. Trelleborg and SKF use "static seals" as a category. Freudenberg breaks it down further into O-rings, X-rings, flange seals, and USIT-Rings. Big brands show that competing in static seals means selling a full set of shapes + groove design + job matching, not just one rubber ring.

Face Seals

International brands usually do not keep it as one fixed product name. They split it by connection type. Parker's Seal–Lok ORFS is a typical commercial name for face seals – it focuses on leak-free connections under high pressure, vibration, and pressure pulses. For simple end covers or face grooves, brands put them under static seals or flange seals instead of creating a new big category.

Flange Seals

This is a sub-category with lots of brand potential. Parker lists flange seals and fastener seals. Freudenberg has flange seals and cover seals. Hutchinson has PFS flange seals and says they can replace wound gaskets and rubber gaskets. Trelleborg's static seal system also includes SAE flange seals. Flange parts are more engineering-focused because they tie closely to flange standards, bolt force, and installation tolerances.

Combined Washers

"Combined washer" is the common Chinese name. International brands break it into composite sealing washers, fastener seals, USIT-ring, or bonded washers. Parker calls them fastener seals / composite sealing washers made of a metal carrier and vulcanized elastomer lip. Freudenberg uses USIT-Rings Fastener Seals. James Walker simply says bonded washers. When making catalogs, keep both the Chinese common name and the international name.

Bonded Seal (metal + rubber combined seal)

This is the most mature and internationally recognized name for combined washers. Trelleborg lists Bonded Seal...

4. Product Tree + International Brand Matching + Material / Application / Difficulty Level

Difficulty level here means "how hard it is to develop and mass-produce." It looks at materials, size and tolerance control, molds, post-processing, whether it is metal–rubber composite, how much it depends on flange/thread/groove matching, and how much application testing is needed.

International brand catalogs do not list everything flat. They manage by two lines at once: one by shape/structure, one by connection/installation method. So it is best to treat "static seal" as an application tag, not as a separate product level.

Product Tree

Standard Seals

  A. Standard Cross-Section Seals

    • O-Ring

    • Encapsulated O-Ring

    • Square Ring

    • D-Ring

    • X-Ring / Quad-Ring

    • Rubber Gasket / Flat Gasket

  B. Connection / Groove Static Seals

    • Static Seal (application tag)

    • Face Seal

    • Flange Seal

    • Combined Washer (Composite / Fastener Sealing Washer)

    • Bonded Seal (metal + rubber combined seal)

Catalog Summary

(1) O-Ring

Benchmark brands: Trelleborg / Freudenberg / NOK.

Main materials: NBR, HNBR, EPDM, FKM, FFKM; also special PTFE-based versions.

Typical uses: oil, water, air, gas sealing in valves, pumps, hydraulics, pneumatics, cars, home appliances, and general factory equipment.

Difficulty: Low.

(2) Encapsulated O-Ring

Benchmark brands: Trelleborg FEP O-Ring / Freudenberg Encapsulated O-Rings.

Main materials: FEP/PFA outer layer + FKM or VMQ core.

Typical uses: strong chemicals, vacuum, flange static seals, high-cleanliness, and food-contact static jobs. International brands stress it is mainly for static use.

Difficulty: High.

(3) Square Ring

Benchmark brands: Trelleborg Kantseal / SKF Square-Rings / Freudenberg Square Rings.

Main materials: mostly NBR, FKM.

Typical uses: SAE flanges, end covers, cover plates for static sealing. Focus on keeping shape and easy assembly.

Difficulty: Medium.

(4) D-Ring

Benchmark brands: Parker D-Rings / Freudenberg D-Rings.

Main materials: same family as O-rings – NBR, FKM, HNBR, EPDM, etc.

Typical uses: radial seals for static, reciprocating, or oscillating jobs. International brands see it as a structural upgrade of the O-ring.

Difficulty: Medium.

(5) X-Ring / Quad-Ring

Benchmark brands: Trelleborg Quad-Ring / Freudenberg X-Rings / Hutchinson JF4.

Main materials: usually NBR, FKM; can extend to other elastomers.

Typical uses: static – flanges, sleeves, end covers; dynamic – hydraulics, pneumatics, reciprocating, rotating, oscillating. Brands highlight lower friction, better sealing, and less twisting than normal O-rings.

Difficulty: Medium-High.

(6) Rubber Gasket / Flat Gasket

Benchmark brands: Freudenberg Gaskets / Flat Gaskets.

Main materials: rubber, fiber, graphite, PTFE, plus industry grades like EPDM, FKM/Fluoroprene.

Typical uses: static sealing between two flat surfaces – flanges, valves, fittings, pump bodies; also chemical, food, beverage, and pharma industries.

Difficulty: Low–Medium (simple flat gaskets = low; industry-specific = medium).

(7) Static Seal

Benchmark brands: Trelleborg Static Seals / Freudenberg Static Seals.

Main materials/structures: covers O-rings, square rings, X-rings, flat gaskets, Bonded Seals, etc.

Typical uses: all no-movement axial or radial seals. Brands treat "static seal" as a category and then list the actual shapes inside it.

Difficulty: Not rated separately – it is really an application tag.

(8) Face Seal

Benchmark brands: Parker Seal–Lok ORFS / Freudenberg Static Axial Seals.

Main materials: usually same as O-ring family; ORFS version is fitting assembly + O-ring seal.

Typical uses: high-pressure, vibration, pulse face connections such as hydraulic pipe fittings, valve block faces, connectors. Internationally these are often named by the connection solution rather than the single ring.

Difficulty: Medium-High.

(9) Flange Seal

Benchmark brands: Freudenberg FLAN89 / Hutchinson PFS Flange Seals.

Main materials/structures: one type is TPU flange seal; another is stainless steel washer + vulcanized elastomer lip.

Typical uses: SAE J518 hydraulic flanges, pipe flanges, bolted flange connections. Brands treat it as a more engineered solution than a plain O-ring.

Difficulty: High.

(10) Combined Washer (Composite / Fastener Sealing Washer)

Benchmark brands: Parker Fastener Seals / Freudenberg Fastener Seals / Hutchinson Banjo Sealing Washers.

Main materials/structures: usually metal carrier + vulcanized rubber lip. Freudenberg standard is NBR + zinc-plated carbon steel, but can extend to FKM, EPDM, Silicone, etc.

Typical uses: bolts, screws, threaded rods, pipe fittings, Banjo fittings to stop leaks.

Difficulty: Medium-High.

(11) Bonded Seal (metal + rubber combined seal)

Benchmark brands: Trelleborg Bonded Seal / Hutchinson Bonded Seal / Freudenberg US Bonded Seals.

Main materials/structures: metal ring/insert + vulcanized rubber body. Metal can be carbon steel, stainless steel, brass, aluminum, etc. Rubber is usually NBR, HNBR, FKM, EPDM.

Typical uses: threaded connections, flange connections, high-pressure hydraulics/pneumatics, fuel, HVAC, fluid transfer. This is one of the most standardized metal–rubber static seals in international catalogs.

Difficulty: High.

One-sentence product line layering

Basic high-volume parts: O-rings, ordinary rubber gaskets / flat gaskets.

Upgrade profit parts: square rings, D-rings, X-rings, combined washers.

High-value parts: encapsulated O-rings, flange seals, Bonded Seals.