Frequent Product Questions

In this section, we address the most frequent questions about our products, to help you find answers and solutions to your challenges easier. If you cannot find an answer below, or you require personal advice, please contact our Product specialists.


How many types of bearings are there?

From a design perspective, bearings are classified into plain bearings and rolling-element bearings. Plain bearings usually have a cylindrical shape and no moving parts. Rolling-element bearings consist of rolling elements such as balls or cylinders which are placed between a turning and a stationary race. You can learn more here.

What is the difference between metric and inch tapered roller bearings?

A tapered roller bearing is made up of an inner ring, an outer ring and in between one or two rows of conical rollers. Metric tapered roller bearings are usually supplied as complete bearings, while inch bearings in cup and cone splits. Depending on the inner size, cups and cones are divided into different series. Within a series you can combine different cups and cones to form a complete bearing. With this concept one can realize bearings with different outer dimensions.

How do you find the right cone and cup combination for a tapered bearing?

If you want to replace an existing bearing, you can check the part numbers on the cone and cup to find the correct replacement products. Be aware that the cone and the cup have different part numbers. If you are looking for a new bearing, you can select the right cup and cone with the help of the desired inner diameter, outer diameter and width.

Which bearing lubricant resists in salt water environments?

For salt water, you can use the bearing lubricant SKF Universal bearing grease LGMT 3 / 0.4.

What is the difference between Cn, C0 and C3?

The letter C is added in the code of a bearing as suffix and represents the clearance. The possible codes are given below.

Clearance symbol Meaning
Cn (C0) Normal radial internal clearance (RIC)
C1 Radial internal clearance smaller than C2
C2 Radial internal clearance smaller than normal
C3 Radial internal clearance greater than normal
C4 Radial internal clearance greater than C3
C5 Radial internal clearance greater than C4

How do you read a bearing designation?

A typical bearing designation contains a combination of digits and letters (5-7) and looks like this: Prefix ABC DE Suffix. Each of these symbols gives specific information about the bearing. The meaning of each position is given below. To learn more, check our Bearing decoding tool.

  • Prefix - Is used for defining the components of a bearing or variations.
  • A - Bearing type
  • B - Width
  • C - Outer diameter
  • DE - Bore diameter
  • Suffix - Indicates design particularities such as the bearing internal or external design, cage design, materials, heat treatment, tolerance, clearance etc. The suffix can be separated from the rest of the designation number by a space, a hyphen or an oblique stroke.

What are the different methods of mounting a bearing?

The choice for a mounting method depends on the bearing type and on the fits. Bearings with cylindrical bores are mounted in most cases by pressing them on the shafts or by heating them, as this expands the diameter. Bearings with a tapered bore can be mounted directly on tapered shafts or cylindrical shafts using tapered sleeves. The table below gives an overview of these methods. To learn more, read our article on Bearing mounting methods.

Mechanical (cold) mounting Hot mounting Hydraulic mounting / oil injection
Bearing size Small, medium Small, medium, large Small, medium, large
Seat type Cylindrical, tapered, adapter sleeve, withdrawal sleeve Cylindrical Tapered, adapter sleeve, withdrawal sleeve
Tools used Fitting tool, hook spanner, impact spanner Hot plate induction heater, hot oil bath Hydraulic nut and pump, drive up method, oil injection method

What are the advantages of ceramic bearings?

Ceramic bearings are lighter than stainless steel bearings and have a higher rolling resistance. Their surface is smoother, therefore friction is reduced and the amount of energy required for rotating the assembly is lower. Harder and more durable than steel bearings, ceramic bearings require less maintenance and don't rust, being a cost-efficient solution.

When is induction heating used for bearings?

Induction heating is used for mounting rolling bearings easier. The device generates a strong electromagnetic field and due to the heat, the metallic bearing expands. This makes it easier to mount it without requiring force. A temperature difference of 90°C between the bearing and the shaft is usually enough for easy installation.

What is the difference between bearing shields and seals?

Both shields and seals are added to a bearing for keeping contaminants out and maintaining the proper lubrication level.

Bearing shields are metallic enclosures that have no contact with the inner ring and therefore have a reduced rotational torque. They are not limited by speed and can be used in high speed applications. Still, if the bearings are mounted in an environment where there is a risk of contamination with fine contaminants, or where the products are exposed to frequent washdowns, then a sealed bearing might be a better choice.

Bearing seals are made from elastomeric materials and can be non-contact or contact by design. Contact seals provide more protection against contaminants, but come with higher friction and rotational torque. So in the end, the choice depends on the application and environment.

How do I choose the right seal for a bearing?

When choosing an external seal for a bearing, you have to consider the bearing type, the lubricant - oil or grease, the physical space available, the shaft surface speed and finish, the seal friction and potential heating, and the acceptable costs.

For example, contact seals are very efficient in preventing fluids or solids from entering the sealed area, but they come in direct contact with the shaft, creating friction and heat. This can damage the shaft finish, making the seal inefficient.

Non-contact seals on the other hand create much less frition and heating, but the lubricant may leak out of the bearing chamber. These seals are therefore more suitable when grease is used.

Bearing isolator seals combine the characteristics of both contact and non-contact seals, offering better protection from contaminants and preventing leakage. Still, they require more space, and are more costly than the other two types.

What bearing materials are suitable for the food industry?

For the food industry, bearings must be produced from high purity materials, the most common one being AISI/ SAE 52100 chrome steel. This material has high corrosion resistance, high and low temperature durability and is lightweight. AISI 440C stainless steel, AISI 304 stainless steel, AISI 630 stainless steel and 1T titanium are also suitable for food applications.

Which bearing materials are suitable for use under water?

In general, ball bearings aren't 100% waterproof and shouldn't be used under water. Still, if the bearing only comes in contact with spray water or is mounted in a humid environment, stainless steel is the recommended material. The grease of the bearing also protects against moisture and water, but keep in mind that the more grease you use, the higher the resistance within the bearing. Additional oil seals should be used for preventing oil loss and the ingress of dirt into the bearing.

As an alternative to stainless steel, you can use ceramic or plastic bearings. These also prevent corrosion and magnetism. However, plastic is only suitable for low loads and ceramics can quickly become porous when worn.

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Sealing and Polymers

What is the shelf life of a rubber seal?

The shelf life of a rubber seal is determined by the specific elastomer that seal is made from. In the table below you can find the shelf life for the most common elastomers used in ERIKS seals and O-rings. For more information, check our O-ring Technical Handbook.

Type of rubber Common / trade name ASTM D1418 abbreviation
Shelf life: 20 years or higher
Silicone Silicone Q
Fluorosilicone Silastic LS FVMQ
Fluorocarbons Fluorel, Viton® FKM
Polyacrylate Acrylic ACM, ANM
Shelf life: up to 10 years
Polychloroprene Neoprene CR
Ethylene / propylene Ethylene propylene EPDM
Ethylene / propylenediene Ethylene propyleneter polymer copolymer EPM
Isobutylene / Isoprene Butyl IIR
Shelf life: up to 5 years
Butadiene / Acrylonitrile Nitrile, NBR NBR
Butadiene / Styrene SBR SBR

What’s the difference between NBR and HNBR?

NBR stands for Nitrile Rubber and is the general term for Acrylonitrile butadiene. Also referred to as Buna N, this copolymer of butadiene and acrylonitrile is the most widely used in the sealing industry, thanks to its properties. The acrylonitrile content may vary from 18% to 50%, the higher this percentage, the better the resistance to petroleum products. NBR can be used at temperatures between -35°C and +120°C, and has good tear and abrasion resistance. NBR is the standard material for hydraulics and pneumatics. NBR resists oil-based hydraulic fluids, fats, animal and vegetable oils, flame retardant liquids (HFA, HFB, HFC), grease, water, and air.

HNBR stands for Hydrogenated Nitrile. It is a highly saturated, oil-resistant elastomer with excellent resistance to heat, ozone and chemicals. This compound has been developed to meet higher temperatures than standard NBR, while retaining resistance to petroleum based oils. HNBR is resistant to mineral oil-based hydraulic fluids, animal and vegetable fats, diesel fuel, ozone, sour gas, dilute acids and bases. HNBR is suitable for high dynamic loads, has a good abrasion resistance and can be used in temperatures from -30°C to +150°C.

How do I choose the most reliable O-ring?

Our O-ring choosing guide helps you on your way by displaying suitable O-rings per industry. To find out which O-ring is right for you, click on the industry that applies to you. The appropriate rubber compounds are then displayed per industry, including the hardness, temperature range and corresponding approvals on the compounds.

When should I use a backup ring?

Back-up rings or support rings are often used in high-pressure applications. It is generally accepted that up to approx. 70 bar an O-ring with a Shore A hardness of 70 will be sufficiently hard at room temperature to prevent extrusion. It is important that the correct clearance is observed. If the pressure in the application is higher than 70 bar, then we advise you to use an O-ring with a hardness of 90 Shore A. In addition, we advise using a back-up ring.

What are AS sizes for O-rings?

There are various standards that apply to O-ring sizes, and these include US Standard AS568, British Standard, Swedish, as well as many common metric sizes according to DIN and ISO standards. The standard sizes in the United States are defined by the Aerospace Standard AS568B, which lists the sizes of O-rings in both inches and millimeters. You can learn more and see the corresponding sizes in our O-ring Handbook.

What is the difference between an O-ring and a Vulc-O-ring?

Vulc-O-rings are produced from extruded cord to a very high technical standard. Unlike O-rings, Vulc-O-rings don't require moulds, so the production costs are lower. Other advantages of Vulc-O-rings include: no upper diameter restrictions, no flash lines, can be used in standard housings and have short lead times. Vulc-O-rings can be made from materials like NBR, FKM A type, FKM GF type, VMQ and EPDM.

ERIKS can produce Vulc-O-rings with cross sections ranging from 1.78 mm to 25.4 mm. These will have a surface finish as extruded unless otherwise requested. Unlike moulded O-rings, Vulc-O-rings have a limit as to how small an inside diameter that can be produced, which is regulated by the cross section.

Which O-ring is suitable for dairy products?

O-rings used with dairy products need to comply with 3A, FDA and EC 1935/2004 standards. These norms ensure that the rubber compounds in the O-rings do not release harmful chemicals. At ERIKS, we use special rubber compounds that are metal- and X-ray detectable.

Why is my O-ring leaking?

O-ring leaks can usually be traced back to three common causes. The main cause is the incorrect sizing of the O-ring combined with the groove dimensions. The second cause of leaks is the excessive stretching or compression of the O-ring. The third cause of leaks is the incorrect choice of material or compound for your application. Learn more here: Prevent damage to your O-ring.

Does a crack change the chemical properties of my O-ring?

If an O-ring starts to have small scratches or cracks, this isn't necessary a problem, as the product remains as resistant to chemical compounds as before. However, O-rings that are in this state are most likely at the end of their life cycle, therefore they will soon have to be replaced. This is because they will lose part of their binding force and will no longer seal perfectly.

How much compression do I need for a good O-ring sealing?

For an effective seal, the internal diameter (I.D.) of the O-ring should be smaller than the piston groove diameter. When the O-ring is used for hydraulic or pneumatic piston sealing applications, the stretch should be 2%-5% for dynamic applications and 2%-8% for static applications. It is not recommended to have a stretch greater than 5% in dynamic applications, as this can create too much stress and accelerate the aging of the O-ring, compromising the seal. An exception is the floating seal, which is used in applications where some leakage is accepted.

How do I choose the right lubricant for an O-ring?

The lubrication of an O-ring is done mostly when the O-ring is installed, as this helps protect the product from damage by abrasion, cutting or pinching. The lubricant also helps protect the surface of the compound against degradation by atmosphere.

When selecting a lubricant for an O-ring, you should consider the additives it contains, which should not cause excessive shrinkage or swelling of the O-ring compound. Also, the lubricant's properties shouldn't change too much over the temperature range, and the fluid should be compatible with the ones being sealed. The lubricant shouldn't pass through filers, shouldn't leave deposits after cycling, and should form a thin film over the metal surface.

When should I use a X-ring instead of an O-ring?

If a part that is sealed with an O-ring makes a sliding movement, the O-ring can also move in the groove and can twist. When an O-ring twists, its surface can get damaged, leading to leakage. An X-ring on the other hand has four sealing lips, so it is more suitable for sealing moving parts. Thanks to its shape, an X-ring requires less compression, therefore the friction and the wear is reduced.

What does the FDA approval of an O-ring mean?

If O-rings are approved by the FDA, it means that they are food-safe and the material does not release harmful substances.

Is EPDM resistant to coolant?

Yes, EPDM is resistant to coolant (high chemical resistance to ethyl glycol, OAT and HOAT coolants).

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Flow Control

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Engines and Power Transmission

How do you calculate the length of a V-belt?

Each belt has its own reference length: with classic belts it is the inner length (Li), with American belts it is the outer length (La) and with other belts it is the primitive length. The primitive length (Lp) is also called cord length, date length (Ld) or working length (Lw). If you are looking for a certain length, it is therefore important to know what length it is exactly. The outside length is actually the only thing you can measure yourself. Unfortunately, with the outer length you often can not immediately find a suitable V-belt belt because the outer length of a V-belt is seldom indicated.

How do I choose the taper lock bush for a gear?

A taper lock bush or taper bush is a locking mechanism used in power transmission drives for locating pulleys, sprockets and couplings to shafts. Thus, the taper bush dimensions depend on the shaft diameter. You can find more information here.

What is the difference between timing belts and V-belts?

A timing belt or toothed belt is a flexible belt with teeth moulded onto its inner surface. It transfers power between two parallel shafts, each shaft having a toothed belt pulley attached. This design is also sometimes referred to as synchronous drive because it has a fixed transmission ratio and prevents slippage. Timing belts are used in a variety of mechanical devices where high-power transmission is desired.

A V-belt has a trapezoidal cross-section shape and just like the toothed belt, it transfers power between two parallel shafts. Each shaft has a V-belt pulley attached, and the belt then connects the pulleys. A V-belt isn't always used for power transmission; sometimes, it is used just for the purpose of transporting products. V-belt drives can slip to a certain extent, but this is not always a problem. In fact, in certain applications it is desirable to have a little slippage, for safety reasons.

When should I choose a timing belt?

A timing belt is used in internal combustion engines to synchronize the rotation of the crankshaft and the camshaft, so that the engine's valves open and close at the proper times. From a design perspective, a timing belt is a toothed belt, meaning a drive belt with teeth on the inside surface. As its name suggests, this type of belt is used for timing purposes, working under a constant speed. Timing belts are preferred in applications where no slip is allowed and a synchronous position of the driven shaft is expected. These belts offer the best efficiency and are cost-effective.

What materials are used in conveyor belts for the food industry?

Conveyor belts used in the food industry must ensure food safety and prevent contamination. Standards that apply include FDA's FCM (Food Contact Material) restrictions, the EU Regulation CE 1935/2004 and Regulation CE 2023/2006, as well as the EU Regulation 10/2011 and the Declaration of Conformity.

Why is the number of teeth in a timing belt important?

Timing belts are used in a variety of devices, but the most common application is for keeping all the moving parts of an engine wroking together in a synchronized manner. For this to happen, the teeth of the timing belt need to interlock perfectly with the cog wheels of the crankshaft and camshafts. When one or more teeth wear out, the belt can slip or it can continue to work, but with improper timing. Even if the belt itself will not break, the lack of synchronization can damage other components in the engine.

If you select a belt that doesn't have the correct number of teeth of your application, then the belt will not have the same pitch as the pulley. As a result, the parts will not engage properly, and the overall performance of the system will be affected. When the belt is chosen correctly, this will result in less wear and thus a prolonged life.

How are V-belts and timing belts maintained?

A preventive maintenance program for belts involves ensuring a safe work environment, regularly scheduling belt inspections, following the proper instructions for installing the belts, and conducting regular belt performance evaluations. Belt storage and handling are also important.

Do I need to lubricate a belt?

Timing belts do not require lubrication. In fact, using lubricant or grease can lead to an accumulation of debris that will slowly wear at the belt material, causing premature belt failure. The same applies for V-belts: they don't require lubricants or grease, and if there's too much noise, the belt probably needs to be replaced, not greased.

What is the difference between a motor, a drive and a drive system?

A motor is the device - mechanical or electrical - that generates the force used for powering a machine. A drive is the device that feeds electricity into the motor, in specific amounts and at specific frequencies. By doing so, the drive controls the motor's speed. A drive system is the assembly formed by the motor and the drive.

Why is my drive belt so noisy?

The most common reasons for noise coming from belts are misalignment and incorrect tension. However, accumulation of debris or small foreign objects that get stuck in the drive system can also cause noise. Another potential cause is the presence of worn out elements.

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Safety Equipment

Which breathing mask is suitable for simple (home) work?

You can use a simple dust mask that meets the protection class FFP1. An example is this dust mask from the brand RX.

What does the N95 standard mean and when does it apply?

The N95 standard is an American standard that corresponds to the filter class FFP2.

Which filter should I use when working with asbestos?

Filters for working with asbestos should comply with the EN143: 2000 standard, and should offer protection against particles up to 50x the limit value. However, this is not a guarantee for 100% protection. While asbestos removal companies use these filters, they also have motor-driven respiratory protection.

Which filter can I use when dealing with fumes and dust particles?

In this case you can use a combination of the 3M particle filter 5925 P2, the 3M 6059 gas and vapor filter and the 3M filter cover 501.

What safety equipment should I wear for work at height?

Fall protection equipment can be classified into personal protection equipment (PPE) and collective protection equipment. Personal protection equipment includes fall arrest systems, positioning systems, suspension systems and retrieval systems. Collective equipment include guardrails, horizontal lifeline systems, safety nets and so on. You can learn more in our Guide to Safety at height.

What are the protection classes of work shoes?

The protection classes for safety shoes are as given below. You can learn more here.

  • SB - Safety footwear with protective toecap which offers resistance against an impact of 200 joules.
  • S1 - As SB, but also meets the following additional requirements: closed seat region, antistatic properties, energy absorption of the heel region.
  • S2 - As S1, with the following additional requirements: waterproofness and water absorption of the uppers.
  • S3 - As S2, with the exception that the following additional requirements are also required: penetration resistant midsole.
  • S4 - Shoes made of 100% rubber or polymer. Safety shoes with steel toe, waterproof and protected against moisture and dirt.
  • S5 - Safety shoe with steel toe cap and steel sole, waterproof and suitable for areas with increased exposure to liquids, moisture and dirt. Additionally protected against entry of sharp or pointed objects.

What are the sizes of work shoes?

You can use the table below to identify the shoe size based on the length and width of your feet. For the length, we use the ISO/TS 19407:2015 Footwear Sizing standard. For the width, the standard size is indicated with the letter "D". XD shoes are a little wider, and XXD shoes are even wider.

Foot size (in cm)
European sizes Foot length (cm) D XD XXD
36 22.6 23
37 23.3 23.4 23.7
38 24 23.8 24.2 24.3
39 24.6 24.3 24.6 24.7
40 25.3 24.7 25 25.2
41 26 25.1 25.4 25.6
42 26.6 25.5 25.9 26.1
43 27.3 26 26.3 26.5
44 28 26.4 26.7 27.1
45 28.6 26.8 27.1 27.5
46 29.3 27.2 27.6 28
47 30 27.6 28 28.4

What are the sizes of protection gloves?

You can find the common glove sizes below. Gloves that are below the minimum length should be called "Fit for Special Purpose". Learn more about safety gloves here.

Glove size Fits hand size Hand circumference/length (mm) Minimum length of the glove (mm)
6 6 152/160 220
7 7 178/171 230
8 8 203/192 240
9 9 229/192 250
10 10 254/204 260
11 11 279/215 270

What are the protection classes of protection glvoes?

The protective capacity of a glove is reflected by its performance level, which is a number between 0 and 5. This number indicates how the glove has performed in a specific test. The meaning of the performance levels is given below. You can learn more about safety gloves here.

Level Meaning
0 The glove is untested or falls below the minimum performance level
1 Minimum protection
2 Good protection
3 Very good protection
4 Excellent protection
X The test method is not suitable for the glove sample

What do the hardness codes of grinding discs mean?

The hardness code of a grinding disc describes the resistance that the binding of the disc exerts against grain shedding. According to standard DIN ISO 525, the bond hardness is identified by a letter from A to Z, where A is the softest and Z the hardest.

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Tools and Accessories

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Dear Customer,

Coronavirus COVID-19 Update: As the UK government has taken the decision to close all non essential retail businesses this is now impacting on manufacturing and supply channels across the globe. We are working with our supply chain to maintain all product supply.

Our Webshop is experiencing a high volume of demand for certain products that are now classified as “RISK” supply lines. Once your order is placed we will review the availability of products and one of our team will contact you to confirm your order.

Thank you for your understanding during this unprecedented time.

Thank you on behalf of ERIKS Industrial Services