In a sense, thrust bearings are 90° angular-contact bearings. They support pure thrust loads at moderate speeds, but for practical purposes, their radial load capacity is nil.
Because they cannot support radial loads, ball thrust bearings must be used with radial bearings. Even slight misalignments can cause drastic load concentrations, so the bearings must be kept square with the shaft or used with self-aligning seats. However, the ability of the self-aligning seat to follow shaft wobble or misalignments is still quite limited.
Flat-race bearings consist of a pair of flat washers separated by the ball complement and a shaft-piloted retainer, so load capacity is limited. Contact stresses are high and torque resistance is low.
The prime advantage of flat-race bearings is they permit eccentricities, because there are no grooves to restrain one race from wandering slightly with respect to the other.
One-directional, grooved-race bearings have grooved races very similar to those in radial bearings. Thrust capacity is about twice that of the flat-race bearing and limiting speed is about three times as high. However, limiting speed is still quite low because balls spin at high speeds.
Two-directional, grooved-race bearings consist of two stationary races, one rotating race, and two ball complements. Their characteristics are identical to those of the one-directional bearing, except they can support thrust in both directions.