Duplexing of Angular Contact Bearings
(See Also: Duplexing of Precision Angular Contact Bearings)

DB back-to-back

DF face-to-face

DT tandem

Angular contact ball bearings may be installed in sets of 2, 3 or more, either all in the same direction to carry heavier loads or in opposing directions to offset opposing loads. Some applications that do not require precision angular contact sets (i.e. irrigation well pumps, etc.) may use standard, individual flush ground angular contact bearings.

Note: Although many applications require individual angular contact bearings that do not need to be flush ground, it is a common practice for U.S. distributors to primarily stock flush ground angular contact bearings. This is done because the distributor may not always know when bearings are installed in sets where uncontrolled end play may cause equipment failure.

Axial loads may be present from either direction; thus angular contact bearings may be mounted in either a back-to-back or face-to-face configuration. In a back-to-back configuration, the set is installed with the large outer ring faces touching; the smaller outer ring faces are turned to the outside of the set; and it is used for added rigidity. This is identified by NTN with the suffix DB.

A face-to-face configuration (the set is installed with the smaller outer ring faces touching and larger outer ring faces turned to the outside of the set) has a larger allowable misalignment angle and is identified by NTN with the suffix DF.

When a very heavy axial load is exerted from one direction only, the bearings are stacked in tandem. Each bearing added increases the load carrying capability of the tandem set. NTN designates with the suffix DT.

Many angular contact bearings are installed in precision sets that normally specify a predetermined amount of preload. This requires additional manufacturing processes where the inner and outer ring faces on each side of the bearing are ground such that when the bearings are assembled as a set, there is a small measured gap remaining between either the inner or outer ring faces.

In the case of a back-to-back arrangement, the gap would be between the inner ring faces when the outer rings are pressed together. In the case of a face-to-face arrangement there would be a small gap between the outer ring faces when the inner rings are pressed together. This small gap is the amount of axial clearance manufactured into the bearing set. As the rings are pressed together during assembly, the gap is eliminated and the bearings are preloaded to provide rigidity and greater running accuracy.

NTN’s suffix designation for preloaded precision sets are N for normal preload, L for light preload, M for medium preload and H for heavy preload.