When angular contact ball bearings are used and require larger axial loads, as shown in the figure, 3 sets of single-row bearing combinations are used. There are 3 combination methods, which are represented by the combination codes DBD, DFD, and DTD. When calculating the fatigue life of this type of precision combined bearing, like single-row bearings or double-row bearings, the equivalent dynamic load calculated from the radial load and the axial load borne by the bearing is also used for calculation. Assuming that the equivalent dynamic load is Pr, the radial load is Fr, and the axial load is Fa, the relationship between the radial equivalent dynamic load and the bearing load will be similar to the following formula. Pr u003d XFr＋YFa(1) where ：X Radial load factor: Y Axial load factor see Table 1 Axial load factor, it will change with the contact angle. Angular contact ball bearings with a smaller contact angle will increase the contact angle when the axial load increases. This change in contact angle can be expressed by the ratio of the basic static load rating Cor to the axial load Fa. Therefore, an angular contact ball bearing with a contact angle of 15° represents the axial load factor of the contact angle corresponding to this ratio. Angular contact ball bearings with contact angles of 25°, 3, and 4 have negligible influence on the axial load factor due to changes in the contact angle, so the axial load factor is regarded as a constant value. In the three rows, 2 sets of bearings bear the axial load type code or DFD. In the three rows, 1 set of bearings bear the axial load type code DBD or DFD.