What Is a Gasket? Gaskets vs O-Rings and When to Use Each

Quick answer: what is a gasket?

A gasket is a flat seal clamped between two surfaces to stop leaks at a joint. Bolts or a clamp squeeze it so it fills small gaps and surface roughness. Gaskets are cut or molded to the joint's shape, from rubber, plastic, composite or metal. An O-ring is different: a round ring that seals in a machined groove.

Not sure which one your joint needs? Send us the details and we'll recommend a part and material.

Gasket vs O-ring at a glance

	Gasket	O-ring
Shape	Flat sheet or ring, cut or molded to the joint	Round ring with a circular cross-section
Where it sits	Between two flat faces, such as pipe flanges or covers	In a machined groove (gland)
How it seals	Bolt or clamp load compresses its whole face	Squeeze across the cross-section; system pressure pushes it harder against the gap
Motion	Static joints	Static, plus rod, piston and rotary seals
Sizing	Custom cut, or standard flange and sanitary sizes	Standard AS568, metric, JIS sizes, and custom sizes
Typical uses	Pipe flanges, covers, tri-clamp fittings, enclosures	Valves, pumps, hydraulic cylinders, connectors

What does a gasket do?

A gasket fills the space between two parts that can never be perfectly flat or smooth. When the joint is bolted or clamped, the gasket compresses into scratches, waviness and tool marks. That compressed layer blocks the leak path for liquid or gas.

Gaskets do more than seal. Depending on the material, they also insulate, cushion vibration and keep dirt and moisture out of enclosures. Our Gaskets and Custom Cutting page lists those jobs by industry, from automotive and aerospace to HVAC, electronics and food processing.

Because a gasket relies on clamp load, the joint must keep it compressed. Uneven bolt torque, a flange that flexes, or a material that relaxes over time can all let a gasket leak.

Types of gaskets

Gaskets are grouped by how they're made and what they're made of. These are the types Canyon supplies most often:

• Flat (sheet) gaskets. Cut from rubber, composite or plastic sheet to seal between two flat faces. See how they're made in our post on cut gaskets and cut components.
• Flange gaskets. Made to ASME B16.21 for standard pipe flanges. Ring (RN) gaskets sit inside the bolt circle; full-face (FF) gaskets include the bolt holes. Both are in our store: ring gaskets and full-face gaskets.
• Sanitary (tri-clamp) gaskets. Hygienic gaskets for food, beverage and pharmaceutical lines, in 40MP, 40MPF and 42MP mini styles. Our sanitary gasket guide covers sizes and compliance.
• Spiral wound and metal gaskets. Used where temperature or pressure is too high for soft materials. See spiral wound gaskets.
• Sponge and foam gaskets. Soft, low-force seals for enclosures, doors and panels.

Have a drawing or an old part with no part number? Our engineering team can identify the material and reproduce it.

What are gaskets made of?

Material is the biggest decision for any gasket. The fluid, temperature and pressure decide it, not the gasket's shape. Common families include:

Family	Examples	Typical use
Rubber (elastomers)	EPDM, nitrile, silicone, neoprene, FKM, FFKM	General sealing; choice depends on fluid and temperature
Plastics	PTFE, filled PTFE, PEEK, UHMW	Aggressive chemicals, low friction
Composites	Aramid or carbon fiber with a rubber binder, graphite	Steam, oils and high-temperature flanges
Metals	Stainless steel, copper, aluminum	High temperature and pressure
Sponge and foam	Closed-cell and open-cell sponge	Low closing force, dust and weather seals

Many of the same compounds are used for both gaskets and O-rings. For example, CP75BK01, a 75 Shore A Canrez® FFKM rated -15°C to 320°C, is sold as O-rings, flange gaskets and sanitary gaskets. EP70BK01, a 70 Shore A EPDM rated -55°C to 130°C (-67°F to 266°F), is a common choice for water and steam.

Compliance matters too. Gasket materials are available to FDA, NSF 51 and 61, USP Class VI and 3-A requirements, among others. If chemicals are a concern, the Chemical Compatibility Table is a good first check against your fluid.

How are gaskets made?

Most gaskets are cut from sheet. Canyon uses CNC knife cutting, CNC laser cutting, water jet cutting and flat-bed die cutting, depending on the material and geometry. Die cutting suits large runs of the same shape; knife and water jet suit prototypes and thick or tough materials.

Gaskets can also be molded, which suits complex profiles and high volumes. Standard flange and sanitary gaskets are made to published dimensions, so they can be bought by size.

Need a gasket cut to a drawing? Request a quote with the file, material and quantity.

Gasket or O-ring: how to choose

1. Check for motion. If a rod, piston or shaft moves against the seal, use an O-ring or another dynamic seal. Gaskets are for static joints.
2. Check for a groove. O-rings need a groove machined into one part. If both faces are flat and you can't add a groove, use a gasket.
3. Check for a standard fitting. Standard pipe flanges use ASME B16.21 gaskets; tri-clamp fittings use sanitary gaskets.
4. Otherwise, an O-ring in a groove is usually simpler. Standard AS568 and metric sizes are stocked, and the groove sets the squeeze for you. Our General Groove Design Guide covers the sizing.
5. Pick the material. Match it to the fluid, temperature and pressure, and test it in the application before production.

Still deciding between the two? Talk to our engineers about your joint and fluid.

FAQ

What is a gasket in simple terms? A gasket is a flat seal squeezed between two parts so liquid or gas can't leak through the joint.

What is the difference between a gasket and an O-ring? A gasket is flat and seals across its whole face when clamped. An O-ring is round and seals in a groove, and it can also seal moving parts.

What are gaskets made of? Rubber, plastic such as PTFE, fiber composites, graphite, metal and sponge. The fluid, temperature and pressure decide which material fits.

Can an O-ring replace a gasket? Sometimes. It needs a groove machined into one of the parts, so it's usually a design change rather than a direct swap.

What does a gasket do? It seals a joint against leaks, and depending on the material it can also insulate, cushion vibration and keep out dust and moisture.

If your question isn't here, email or call us and an engineer will answer it.

Find gaskets and O-rings

Standard flange gaskets, sanitary gaskets and O-rings are priced online with live stock in the Canyon store. For custom cut gaskets, molded parts or materials you don't see, request a quote or contact us.