The axial bearing may be stiff or aligning, single or double-acting (in one or two directions). The rolling elements may be balls, cylindrical rollers, needle rollers, tapered rollers and tapered barrel-shaped rollers, and are always arranged within a cage. The rings are washers with raceways; in the aligning versions, there are check washers with hollow spherical surface, within which the real washer is able to oscillate, thanks to its own outer concave spherical finish.
In the case of tapered barrel-shaped rollers, it is the actual washers themselves that have concave spherical surfaces to enable oscillation. They are always used together with bearings that are able to sustain radial loads; they must always be assembled to guarantee continuous contact between washers and rolling elements.