Internal clearance is the amount of internal free space between the rolling elements and the raceways of a bearing. The ranges of internal clearance are governed by ISO and the ABMA and are denoted by the NTN suffixes: C1, C2, C3, C4 and C5, where no suffix indicates normal clearance. C1 is a range less than C2. C2 is a range less than normal. C3 is a range greater than normal, C4 is a range greater than C3 and C5 is a range greater than C4.

Precision is a range of tolerance on bearing dimensions. ISO and ABMA govern the precision ranges. ISO uses Class 0, Class 6, Class 5, Class 4, and Class 2 and ABMA uses ABEC 1, ABEC 3, ABEC 5, ABEC 7 and ABEC 9, respectively the systems are generally interchangeable. NTN uses P0 (usually not added to the part number), P6, P5, P4 and P2 to denote Class 0, Class 6, Class 5, Class 4 and Class 2, respectively.

Ultimately, clearance does not affect tolerance and tolerance does not affect clearance. (TOP)

C3 is typically not referred to as a fit; it is the internal clearance in the bearing as defined above. A bearing fit is how tight or loose the shaft and housing hold the bearing in place.

When either of the rings of a bearing is tight fitted to its mating component (i.e. the shaft or housing), the resultant deformation of the ring causes a reduction in the amount of clearance in the bearing. A rotating bearing also produces heat due to material stress and through friction from rolling and sliding contact, lubricant shear, and seal contact. The bearing housing is usually stationary and is therefore better able to conduct heat away from the outer ring of the bearing. As a result, the temperature of the inner ring and rolling elements is usually 5℃ to 10℃ higher than that of the outer ring. This results in greater thermal expansion of the inner ring and thus reduces the clearance in the bearing. If the shaft is being heated or if the housing is being cooled, the temperature difference will be even greater.

Selection of the proper initial bearing internal clearance must take all the foregoing factors into consideration. Assuming this has been done, it is never advisable to replace a bearing with one having a lower initial clearance. By the same argument, it is usually safe to substitute a larger clearance when the desired clearance is not available. (TOP)

Preload is an initial load or "negative clearance" given to a bearing before operation. This results in the rolling element and raceway surfaces being under constant elastic compressive forces at their contact points. This has the effect of making the bearing extremely rigid so that even when load is applied to the bearing, radial or axial shaft displacement does not occur. (TOP)

The "LB" seal is a non-contact seal for reduced torque or higher speed requirements. The "LU" seal is a contact seal for better contamination control, but the contact friction increases torque and lowers the limiting speed. (TOP)

NTN does provide field support to its customers. Contact the nearest NTN branch to arrange a visit. (TOP)

A deep groove ball bearing is a non-separable type ball bearing with the line connecting contact points of the steel ball and the raceways of 0° in the radial direction. They are designed to take mainly radial loads but can handle some axial load in either direction. An angular contact bearing is also a non-separable type. The line connecting contact points of the steel ball and raceways create an angle with the line drawn in the radial direction called the contact angle. In addition to radial loads, an angular contact bearing can accommodate relatively heavy axial loads in one direction. The larger the contact angle, the larger the axial loading capacity becomes. Angular contact ball bearings are offered with a 15°, 30° (or) 40° contact angle. (TOP)

Back-to-back (DB) or face-to-face (DF) are duplex arrangements of angular contact bearings (that can also refer to tapered roller bearings). Radial loads and axial loads in either direction can be accommodated by these arrangements. DB should be selected when shaft mounting rigidity is the primary factor. Select DF when shaft misalignment is a concern. The DB arrangement requires the inner rings to be clamped whereas the DF arrangement requires the outer rings to be clamped. (TOP)

NTN tapered roller bearings with the prefix 4T- or ET- and all NTN-Bower TRBs are Timken interchangeable. Please note that it is not recommended to mix TRB components between different manufacturers. (TOP)

In general, steel varieties which can be hardened not just on the surface but also deep hardened by the so-called "through hardening method" are used for the raceways and rolling elements of bearings. Foremost among these is high carbon chromium bearing steel, which is widely used. Case hardened steel has excellent efficiency against shock loads because of its combination of a hard surface layer which has been carburized and hardened to an appropriate depth and a relatively pliable inner core. NTN uses case hardened steel for almost all of its tapered roller bearings and is denoted in NTN nomenclature with 4T- or ET- prefixes. (TOP)

Both NTN and NTN-Bower make 2 and 4 row assemblies, some of which can be found in the NTN-Bower catalogue and the NTN Large Bearing catalogue (2250/E). (TOP)

NTN does make some select sizes of TRBs in high precision classes (i.e. -3, -0, -00, etc.). (TOP)

End play is application specific, or preset in the case of NA type tapered assemblies. The machine manufacturer's recommendations should be followed. For new designs please contact NTN engineering. (TOP)

The "B" type spherical has asymmetric rollers guided by three fixed inner ring ribs that provide better skewing control. The retainer in this bearing is finger type and provides optimum lubrication access. The "C" type spherical employs symmetric rollers and utilizes a floating center guide ring. As no fixed guide rings are used in this design, a window type cage is necessary to guide the rollers. (TOP)

NTN's standard spherical roller bearing, over 50mm bore, is a B-type design. This type of bearing has asymmetric rollers that have the advantage of reduced roller skewing. This allows the bearing to run cooler at higher speeds than other spherical designs. (TOP)

Please download the NTN Information Kit. The interchange section has an area defining NTN nomenclature. (TOP)

NTN follows the ISO precision tolerance classes of P0, P6, P5, P4 and P2 which are equivalent to ABMA classes ABEC 1, ABEC 3, ABEC 5, ABEC 7 and ABEC 9. (TOP)

L1 is typically used to designate a bronze cage for most bearings except for cylindrical roller bearings where G1 is more common. (TOP)

A tapered bore on any NTN bearing is a K (1 to 12 ratio) or K30 (1 to 30 ratio) suffix. The taper ratio is applied over the bore diameter. (TOP)

V#, where # is a whole number, indicates a variation on the basic part number. This suffix does not indicate any specific feature(s), therefore a drawing will be required to determine the special features. (TOP)

NTN has close to 700 greases listed. To choose one for a specific application requires application information. Check with NTN technical support for any special requirements. (TOP)

For general applications a grease fill of 30% of the free space in the bearing seems to be accepted as standard by most manufacturers. Slow speed applications in harsh environments (such as agricultural machinery) can sometimes require a larger fill. High speed applications (i.e. hand tools) can require a lesser fill. Check with NTN technical support for any special requirements. (TOP)

NTN distributes NTN Bearing Unit grease in 400g cartridge format. Standard bearing unit inserts are prelubricated with a lithium base grease (Shell Alvania 3). If NTN Bearing Unit grease is not available at the time of relubrication, one can use a grease with the same base (lithium) and an NLGI grade 2 or 3. (TOP)