NSK 3204 J Schrägkugellager (20x47x20,6)

As a double-row angular contact ball bearing, this bearing carries radial loads and axial loads in both directions, and needs no second bearing to oppose it. The mounting dimensions are 20x47x20.6 mm and the weight is 0.168 kg; technical details beyond these are shown in the specification table. The axial internal clearance of this design is fixed in manufacture and can no longer be adjusted on assembly; fits and adjacent parts have to preserve it, not change it.

A double row angular contact ball bearing is built like two opposed ball sets in a single bearing: the contact lines of the two raceway pairs are inclined in opposite directions and diverge outwards, which corresponds to a back-to-back arrangement of a paired bearing set. The load behaviour follows from that geometry. Radial force is shared between the two ball rows; axial force in either of the two directions is carried by one of those rows; and because the lines of force action span a wide support base, the bearing also takes tilting moments.

The shaft is therefore located in both directions at a single bearing position — the second position can be a purely floating bearing and carries no axial force. The axial internal clearance follows from the ring geometry and is fixed in the factory, not on mounting. Setting it through an adjacent bearing position, through shaft nuts or through unusually tight fits is therefore neither necessary nor permissible: both rings are supported over their full seat and mounted with the fits normal for the load case, so that the built-in clearance is preserved.

This design tolerates misalignment within narrow limits only, because an angular deviation is distributed unevenly over the two ball rows; the seats in shaft and housing should be aligned and geometrically accurate accordingly. The design is common in gearboxes and worm drives, on pump and fan shafts, in agricultural machinery and in wheel bearing arrangements.