Matched bearing

Bearing, set pair mounted ( QJ 315 N2 and NU 315 ETVP2 ), FAG no. 5800770 D
Bearing, 31315 A100 140 N11 CA, each set consists of two bearings and one spacer ring in-between.

Single row angular contact ball bearings are scarcely used individually, and they are usually used in two or more configurations.
High-precision matched angular contact ball bearings are commonly used on machine tool spindles and have a preload. There are three different types of pairings:
DB back-to-back configuration
DF face-to-face configuration
DT series configuration
In addition, there is also a universal assembly type bearing
DU can be back-to-back, face-to-face, and tandem assembly.