Shaft seals, also known as oil seals or simmerings, are essential components used to seal rotating shafts in vehicles, machinery and industrial equipment. They prevent lubricant leakage and protect systems from dirt, dust and moisture.
This guide explains shaft seal types, materials, designations, directional seals, OE numbers and correct measurement to help you select the right seal.
Contents
- Types of Shaft Seals (Simmerings)
- Designations in the Seal Code
- Seal Materials
- What Does the Seal Colour Mean?
- Directional Oil Seals
- OE Number of an Oil Shaft Seal
- Oil Seal Dimensions – How to Measure?
- Inch Shaft Seals
Types of Shaft Seals (Simmerings)
Below are the Corteco shaft seal types with brief descriptions of construction and typical applications.
ASL designation for steering seals → click here
Shaft Seal Type BA
Other designation: SC or IN
External surface coated with elastomer.
Can be used in housings with a relatively rough bore surface.
Shaft Seal Type B1
Other designation: SB, SB2 or TB
Type B according to DIN 3760.
Used where high axial ejection forces on the seal from the housing may occur.
Shaft Seal Type B2
Other designation: SA2
Type C according to DIN 3760.
Typically used in larger sizes. Application similar to B1.
Shaft Seal Type BASL
Other designation: TC
Type AS according to DIN 3760.
For directional seals you may also see the following designations:
RHTC = BASLRD (right-handed)
LHTC = BASLRS (left-handed)
Shaft Seal Type B1SL
Other designation: TB2 or TB3 (lip oriented inwards)
Type BS according to DIN 3760.
Shaft Seal Type B2SL
Other designation: TA2
Type CS according to DIN 3760.
Shaft Seal Type B1BA
Shaft Seal Type B1BASL
Shaft Seal Type BAB
Shaft Seal Type BABSL
Other designation: TCV
Used in very narrow sealing applications.
Shaft Seal Type BAD
Shaft Seal Type B1D
Shaft Seal Type BADUO
Other designation: DC
Shaft Seal Type B1DUO
Other designation: DB
Shaft Seal Type B1BADUO
Shaft Seal Type BAOF
Other designation: VC
Shaft Seal Type B1OF
Other designation: VB2
Shaft Seal Type COMBI
Mainly used in vehicles and agricultural machinery under heavy contamination.
Available in versions from SF1 to SF19: the higher the index, the greater the permissible contamination and moisture level. Depending on version, outer surface can be metal or metal-elastomer, and the actual shaft seal may be single or DUO.
Exact construction is specified in the product description.
Cassette Seal RWDR-K7
Typically used in heavy construction and agricultural machinery operating under high loads and contamination.
Effectively protects shafts, engines, gearboxes and axles from dirt and water.
Seal CS
Seal CSWS
Shaft Seal SCJY
External surface made of elastomer.
Designations in the Seal Code
Seal part codes often include additional suffixes/markers. The most common are:
- SL – with dust lip
- X6 – with double dust lip
- RD – right hand helix (alternative designation: RH)
- RS – left hand helix (alternative designation: LH)
- DRW – bidirectional seal
- X7 – grooved external elastomer surface
- FT – with fixing sleeve
- VI – made of Viton®
For example:
BASLRS X7 FT – indicates a left-handed (RS) BASL shaft seal with grooved external surface (X7) and a fixing sleeve (FT).
BAVISL DRW X6 X7 – denotes a bidirectional (DRW) BA seal in Viton® (VI), with double dust lip (X6) and grooved external surface (X7).
Seal Materials
Seal made of NBR
NBR (nitrile rubber, acrylonitrile–butadiene rubber) is a material with good oil resistance commonly used for shaft seals. NBR seals are typically used for drive shafts and axles as well as in low-temperature industrial applications.
Operating temperature range:
- Maximum: +100°C (+80°C for oil under heavy load)
- Minimum: -40°C
Abrasion resistance: very good
Resistance:
- mineral oils and greases
- vegetable oils and animal fats
- light fuel oils
- non-flammable hydraulic fluids (oil–water emulsions, water–polyalkylene glycol mixtures)
- water up to 60°C
- dilute acids and alkalis at low temperatures
Note that NBR is not resistant to ozone and weathering, so it should not be used in locations exposed to UV radiation.
Seal made of FPM (FKM) – Viton®
FPM (also FKM) — known commercially as Viton® — is a fluorocarbon elastomer with excellent overall chemical resistance and high-temperature performance. FPM/FKM seals are typically used in engine applications.
Operating temperature range:
- Maximum: +200°C (short-term), +150°C (continuous)
- Minimum: -25°C
Abrasion resistance: very good
Resistance:
- synthetic oils
- mineral oils and greases including additive packages
- synthetic fire-resistant hydraulic fluids
- organic solvents
Seal made of ACM
ACM (polyacrylate rubber) offers good oil resistance and elevated temperature capability.
ACM seals are typically used in older engine types, gearboxes and transmissions.
Operating temperature range:
- Maximum: +150°C
- Minimum: -30°C
Abrasion resistance: moderate
Resistance:
- engine and transmission oils
- oils with additive packages
- hydraulic fluids
Seal made of PTFE
PTFE (polytetrafluoroethylene, Teflon) exhibits one of the best chemical and temperature resistance profiles. PTFE seals are typically used in engine applications.
Operating temperature range:
- Maximum: +200°C
- Minimum: -80°C
Abrasion resistance: good
Resistance: not resistant only to molten alkali metals such as sodium or potassium, high-temperature fluorine gas and hydrogen fluoride.
PTFE seals require a perfectly smooth shaft — although chemically and thermally robust, they are very sensitive to installation damage and scratches.
Seal made of PU
PU (polyurethane) seals are used mainly in heavily contaminated environments, though more frequently in hydraulic seals than in rotary shaft seals (e.g. cylinders, guides, pistons).
Examples include construction, agricultural and forestry machinery.
Operating temperature range:
- Maximum: +90°C
- Minimum: -25°C
Abrasion resistance: excellent
Resistance: mineral oils and greases.
Seal made of HNBR (NEM)
HNBR (hydrogenated nitrile butadiene rubber), also marketed as NEM, combines the oil resistance of NBR with improved thermal and chemical stability.
HNBR seals are used e.g. in power steering systems (rack-and-pinion steering, power steering pumps) as pressure seals.
Operating temperature range:
- Maximum: +150°C
- Minimum: -40°C
Abrasion resistance: moderate
Resistance:
- gear oils
- greases, mineral and synthetic oils
- automatic transmission fluids
Seal made of VMQ
VMQ (silicone rubber) is commonly referred to as silicone.
Silicone shaft seals are used in some older types of axles and shafts.
Operating temperature range:
- Maximum: +180°C
- Minimum: -50°C
Abrasion resistance: moderate
Resistance: good resistance to temperature and aging, but poor resistance to most oils (especially transmission and mineral oils — therefore not used in gearboxes). Silicone seals are only used where high temperature is required and oil exposure is minimal.
Seals made of multiple materials
For special design and service requirements, seals are sometimes manufactured from two or more different materials.
Common combinations include PTFE/ACM, FPM/ACM and FPM/NBR.
What Does the Seal Colour Mean?
The colour of a shaft seal typically reflects the base material used. However, this is not an absolute rule — colour also serves as a manufacturer-specific identification aid.
Most commonly encountered seal colours:
- Blue – NBR
- Brown – FPM (FKM) – Viton®
- Black – ACM (sometimes also NBR)
Remember that colour is not a technical standard — the same material may be produced in different colours depending on the manufacturer.
Directional Oil Seals
In order to improve the efficiency of shaft sealing rings, also known as oil seals, spiral grooves (helix-shaped grooves) are sometimes applied to the sealing lip edge on the so-called air side. This design creates a hydrodynamic pumping effect that throws leaking oil back toward the fluid side. At the same time, power losses and friction between the sealing lip and the shaft are reduced.
Sealing lips equipped with grooves are referred to as hydrodynamic lips. The helix direction is matched to a specific shaft rotation direction, therefore such seals are designated as:
- left-hand helix (RS)
- right-hand helix (RD)
For applications where the shaft operates in both directions of rotation, grooves designed for bidirectional operation are used, and the seal is designated as bidirectional (DRW).
Many shaft seals intended for bidirectional rotation do not have grooves. In such designs, lubricant retention is ensured by a standard sealing lip without a hydrodynamic effect. These seals are described as non-directional or have no additional directional markings.
Selecting the correct helix orientation for a shaft seal
To correctly select the helix orientation of the sealing lip grooves, the shaft rotation direction must be determined by observing it from the air side (dry side) of the seal:
- Clockwise shaft rotation → right-hand helix seal (RD)
- Counter-clockwise shaft rotation → left-hand helix seal (RS)
In some cases, the seal may feature a marking or a visible spiral pattern; however, the most reliable method of identification is always to verify the actual shaft rotation direction. The characteristic grooves of the sealing lip “point” in the direction of rotation, making it easier to identify the correct type of seal.
OE Number of an Oil Shaft Seal – What It Is and Why It Matters
The OE number (Original Equipment number) is the original part reference assigned by the vehicle or machine manufacturer. It serves as a unique identifier that helps determine whether a specific oil seal (simmerring) is compatible with a given model.
Manufacturers do not produce oil seals themselves – they source them from specialized suppliers such as Corteco, which provide components for original equipment (OE). The same oil seal can be used across many different vehicles and machines, which is why it may have one or several OE numbers in addition to the manufacturer’s part number.
These OE numbers appear in the table at the end of each product description. You can also enter the OE number in our seal search tool to quickly find the correct part.
For simple oil seals, selecting the correct part based on dimensions, design, and material is usually sufficient. For more advanced seals – such as cassette seals, composite seals, or seals with an integrated flange or sensor – it is strongly recommended to verify compatibility using the OE number.
Where can you find the OE number?
- On the old oil seal – the OE number may be printed or stamped on the part.
- At an authorised service centre – they have full technical documentation and can provide the OE number.
- In online parts catalogues – enter your machine model to obtain the OE reference. Try searching: “parts + manufacturer + model”.
Why should you keep the OE number?
Once confirmed, save the OE number for future maintenance. Oil seals are wear parts and will need replacement again over time.
Oil Seal Dimensions – How to Measure?
An oil seal can be measured very easily using a caliper. To determine its dimensions, measure:
- inner diameter (d)
- outer diameter (D)
- width / height (b)
Please note that some oil seals are stepped or feature protruding elements (e.g. a dust lip). In such cases, the outer diameter or width (height) may occur in two values, e.g. D1/D2 and b1/b2. Examples: 125x160/190x18/20, 12x27x9/10, 139x175/205x11/16.3.
Examples of oil seals with double dimensions
Oil seal with a protruding dust lip and double width dimension b1/b2:
Stepped oil seal with double outer diameter dimension D1/D2:
In the search engine, only the first dimension is always entered.
Most common measurement mistakes
- using a ruler or tape measure – measurements are inaccurate
- providing “approximate” dimensions – this makes correct seal selection impossible
Remember: the purpose of oil seals is precise sealing. The dimension must perfectly match the shaft diameter (inner diameter).
The exact dimension, and sometimes the original equipment number (OE), can be found on the seal surface, although this is not always the case.
Inch Shaft Seals
For seals used in American or British vehicles and in construction/agricultural machinery, you may encounter inch dimensions. To convert inches to mm use the following conversion factors:
- 1 inch = 25.4 mm
- 1 mm = 0.0394 inch