SKF single row Angle contact ball bearing
Single row SKF angle contact ball bearings http://www.alierbearings.com/brand/skf/index13.html  can only carry axial load in one direction, when bear radial load, will cause the additional axial force, must be applied to the corresponding reverse load, therefore, this kind of bearings are generally used in pairs.
Double row angular contact ball bearings can withstand the bigger radial direction load primarily radial, axial two-way joint load and torque load, it can limit shaft or shell two-way axial displacement, the contact Angle of 30 degrees. 
SKF contact ball bearings in pairs
In pairs, the contact ball bearing can withstand the radial load as well as the axial and axial joint load, and can also bear the pure radial load.
The tandem configuration can only bear axial load in a single direction, while the other two configurations can bear axial load in either direction.
This type of bearings in general by submitting users, manufacturers matching combination pairs after installation preloading interference, ring and ball in the axial preload charge state, thus increasing the support stiffness and the whole bearing as a single rotation accuracy.
Back to back configuration, the rear code is DB (such as 70000/ DB), and the load line of the bearing with back pair is separated from the bearing axis.
It can withstand the axial load on both directions, but the load in each direction can only be borne by one bearing.
The bearing with back to back is provided with rigid and relatively rigid bearing configuration, and can withstand overturning moment.
Face to face configuration, the rear code is the DF (such as 70000/ DF), and the face-to-face pair of bearing's load line meets the bearing axis.
It can withstand the axial load on both directions, but the load in each direction can only be borne by one bearing.
This configuration is not as rigid as back-to-back pairs and is not suitable for the overturning moment.
The rigidity of this configuration and the ability to withstand the overturning moment are not as good as the DB configuration, bearing the bearing can withstand the axial load;
In series configuration, the postcode is DT (such as 70000/ DT), in series configuration, the load line is parallel, and the radial and axial load are evenly Shared by the bearing.
However, the bearing group can only bear axial loads acting on one direction.
If the axial load is acting in the opposite direction, or if there is a composite load, a third bearing that is adjusted for a relative tandem bearing must be added.
This configuration can also connect three or more bearings at the same support, but can only bear the axial load of one direction.
Normally, in order to balance and limit the axial displacement of the shaft, the other one shall be fitted with bearings that can withstand another axial load bearing