Glossary of Gaskets

Below is a general list of gasket glossary terms we use here in the manufacture of gaskets.

[accordion title=”General Gasket and Jointing Terms” close=”1″]General gasket and jointing terminology

Gasket and joints:

A generic term for a part the fits between two pieces of metal, typically for sealing purposes. Gaskets are commonly, although not always, made of flexible and compressible material.

Table/ Flange Dimensions:

These define gaskets to fit particular flanges. Example A.S.M.E. standard type joints have class ASA 150# / A.S.A. 300#, DIN standard type joints have class PN 10 / PN16,  and BS Table joints have flange dimensions to Table “H” etc.).

Pipe Gaskets:

Pipe gaskets are those which fit the standard range of pipes, and are specified by their bore size, thickness, table/ class and style i.e. Full Face (F.F.) or Ring style (I,B,C,) to suit raised face joints.


Generally the gaskets are manufactured as a “one off” to suit irregular shaped sealing face.

Pressure Rating:

The pressure the material can seal against.


The bore specifies the inner dimension (I.D.) of the gasket.


The class of a gasket specifies its standard sizes/ rating (E.g. PN 10, PN 16, Class ASA 150#, and Table “H” etc.).
[accordion title=”Technical Gasket Measurement Terms” close=”1″]Technical gasket measurement terminology

Outer Diameter (O.D.):

The outer diameter specifies the outer diameter of the gasket.

Inner Diameter (I.D.):

The inner diameter specifies the inner dimension/ bore size of the gasket.

Pitch Circle Diameter (P.C.D.):

The circle passing through the centre of the bolt holes (for example, eight holes equally spaced on a 200mm P.C.D.).

Inner Bolt Circle (I.B.C):

Inner bolt Circle (I.B.C.) gaskets and joints, fit within the inner diameter of the bolts. Also known as raised face joints (R.F.)

Full Face (F.F.):

Full faced (F.F.) gaskets and joints cover the full face of the flange and have bolt holes which allow bolts to be fitted through the flanges and gaskets, often used on flat faced flanges.


The thickness of the gasket. It is generally recommended to select the thinnest gasket possible subject to the application. The pressure on the gasket will increase in proportion to its thickness.
[accordion title=”Semi-Metallic Gaskets and Joints Terms” close=”1″]Semi-metallic gaskets and joints terminology

Spiral Wound Gaskets (S.W.G):

Spiral wound gaskets are made of a metal coil, or winding, with a material filler. Spiral wounds allow for a higher bolt loading of the pipe flanges. Spiral wounds can withstand very high pressures.

Stainless Steel (S.S.):

Stainless steel is a steel alloy resistant to corrosion. Generally S.S. 316l is used on the inner support ring and on the winding material.

Carbon Steel (C.S.):

Carbon steel is steel in which the main alloy is carbon. Carbon steel is used to manufacture spiral wound gaskets, generally on the outer centering ring.

Graphite Filler:

Graphite is a gasket material commonly used with steam.

PTFE Filler:

PTFE is a plastic used for making gaskets. PTFE is extremely chemically inert, and as such is resistant to chemicals and corrosives. PTFE also has a low co-efficient friction.

Ring Joint/ Ring Type Joint (R.T.J):

Is a metal ring with a cross section which is either oval or octagonal. The most common RTJ joints are manufactured in soft iron or stainless steel.

Type R:

Spiral part only. Commonly used for valves bonnets.
[accordion title=”Non Asbestos Fibre Gasket Terms” close=”1″]Non asbestos fibre gasket terminology

NAF Gaskets (Non-Asbestos Fibre):

Non-asbestos materials replace asbestos gasket materials (CAF). The materials typically have a non-asbestos fibre e.g. Kevlar, glass, or carbon base.

Rubber Binder:

Binds and adheres the fibres together. Most common will be nitrile rubber, due to its oil resistance properties.

CAF Gaskets (Compressed Asbestos Fibre):

This gasket is carcinogenic and hence most industries have started to reduce this material usage

Grade Y:

This grade of gasket materials meets the requirements for British Standard BS7531 Grade Y. These materials are generally suitable for use up to a pressure grade of 70 bar and to 350 degrees centigrade (°C).

Grade X:

This grade of gasket material meets the requirements for British Standard BS7531 Grade X. These materials are generally suitable for use up to a medium pressure grade of 100 bar and to 400 degrees centigrade (°C).
[accordion title=”Rubber Gasket Terms” close=”1″]Rubber gasket terminology


Is an elastic type polymer material that comes in natural and synthetic compositions.

Shore hardness:

Shore A, (otherwise known as durometer), specifies the hardness of material (e.g. 70 SH).


Viton is a synthetic rubber used to manufacture gaskets. Viton can withstand temperatures up to 250°C, and is a very inert but expensive rubber. Viton gaskets are typically used in extreme environments, in the presence of acids and corrosives.


EPDM is a synthetic rubber used to manufacture gaskets. EPDM gaskets are suitable for use with water; a grade for use with drinking water is also available. EPDM is suitable for use up to 120 degrees centigrade (°C).


Neoprene is a synthetic rubber used to manufacture gaskets. Neoprene gaskets are commonly used for exposed environment applications, such as those involving sea water and also has good gas tightness properties.


Silicone is a synthetic rubber used to manufacture gaskets. Silicone can withstand 200°C, widely used in the food processing industry.


Nitrile is a synthetic rubber used to manufacture gaskets. Nitrile gaskets are commonly used for applications involving oils and fuels.

White Food Quality (W.F.Q.):

Most commonly used in Nitrile, Neoprene and Silicon rubbers suitable to be used in food industry.
[accordion title=”Alternative Gasket Material Terms” close=”1″]Alternative gasket material terminology


A gasket material manufactured from the cork wood. Cork material is typically combined with rubbers to give it greater resistance to chemicals and solvents. Cork is a low compression jointing.

Foam / Sponge:

Foam, or sponge, is rubber that has been formed into an air-filled matrix structure. It is typically used to manufacture environmental, and dust, seals for equipment. Generally there are closed and open cell type sponges. Closed cell repel moisture, whereas open cell absorb moisture.

O- Ring:

An O-ring is a loop of rubber / elastomer with an o-shaped cross-section. The measurements required are the inside diameter of the O-ring & cross-sectional diameter of the chord. These are also manufactured from PTFE for exceptional chemical resistant properties.


Gasket paper, otherwise known as cellulose paper or oil paper jointing, is a paper impregnated with chemicals to make it resistant to oils, fuels, and solvents and commonly used in low pressure and low temperature applications as an economical alternative to NAF.

PTFE Envelope:

A PTFE Envelope is an ‘envelope’ of PTFE designed to line the bore of a pipe gasket. PTFE is an extremely inert material but it is also comparatively expensive. Having a PTFE bore-liner is therefore a way of gaining the chemical resistance of PTFE without the associated costs. Such envelopes can be fitted to rubber, or non-asbestos type gaskets.
[accordion title=”Typical Gasket Applications Terms” close=”1″]Typical gasket applications terminology

  • Engine and Head gaskets
  • Intake & exhaust gaskets
  • Motorbike and Moped gaskets
  • Heat Exchanger gaskets
  • Valve gaskets
  • Pump gaskets
  • Pipe work gaskets
  • Hose gaskets
  • Hatchway gaskets
  • Port hole gaskets
  • Manway gaskets
  • Boiler gaskets
  • Gearbox gaskets
  • Sump gaskets
  • Reactor gaskets
  • Tank gaskets
  • Turbine gaskets