Back-to-back duplex arrangement Bearings (also known as “DB arrangement”, “O arrangement”) is a type of duplex bearing arrangement where the two half are placed so that contact angle lines of the bearing diverge inwardly.

Duplex bearings are a set of two bearings  on a shaft with the inner and outer rings clamped together with preload to attain greater axial and radial rigidity. Duplex bearings also used to achieve additional capacity when insufficient space radially for larger bearings.

Duplex bearings are machined as matched sets.  The pairs are furnished with the race faces ground to provide preload when installed. To accomplish this, a gap is provided between the inner races or outer race of the pair. When the bearings are installed and clamped axially, the gap is closed producing a preload on the bearings. There are three types duplex bearing arrangements commonly used and they are Back to Back, Face to Face and Tandem bearing arrangement. Bearings that are normally duplexed are angular contact ball bearings and tapered roller bearings.