Angular  contact  ball  bearings  are particularly suitable for carrying combined (axial and radial) loads. Sometimes, they also can carry pure axial load and operate in higher speed. Under radial load, axial component force will be produced which must be counteracted. So the bearings are normally adjust against a second bearing.   

Since these bearing have a contact angle, they can sustain significant axial loads in one direction together with radial loads. Because of their design, when a radial load is applied,  an axial force component is produced; therefore, two opposed bearings or a combination of more than two must be used.