To increase the load capacity and rigidity, the angular contact ball bearings for machine tool spindle are usually matched in pairs or set of more units.

Every single bearing to be matched should meet the requirements of boundary dimension tolerances and running accuracy, besides, there are high requirements for the following performance parameters between any two bearings:

(1) Mean bore diameter difference between any two bearings.

(2) The radial runout difference of inner rings between any two bearings.

(3) Mean outside diameter difference between any two bearings

(4) The radial runout difference of outer rings between any two bearings.

(5) Actual contact angle difference between any two bearings.

(6)The protrusion difference between any two adjacent bearings.

Duplex arrangement bearings have three kinds of configuration, back-to- back (DB), face-to-face (DF) and tandem (DT).