Accommodate axial displacement internally, rather than requiring the outer ring to slide in its housing.

Both types accept angular misalignment - that is what the concave outer raceway gives them. The difference is what happens when the shaft grows.

A spherical roller bearing has a fixed axial relationship between its rings. To allow shaft expansion it must be mounted with a sliding fit so the outer ring can move in the housing. That sliding is metal on metal, it can stick through fretting, corrosion or contamination, and when it sticks the thermal growth is resisted and generates axial load on both bearings.

A toroidal bearing's rollers can move axially along the raceways while continuing to roll. The displacement is taken up inside the bearing by rolling contact, so both rings can be fitted tightly and there is no sliding interface to seize.

On a hot, long or heavily loaded shaft that is a meaningful reliability difference.

In the non-locating position only, paired with a locating bearing at the other end.

A shaft needs one bearing that fixes it axially - the locating bearing, which takes any thrust and defines the shaft's position. The other bearing must allow the shaft to grow and shrink without loading anything.

A toroidal bearing is designed for that second role. Because its rollers can travel axially, it carries essentially no axial load and will not restrain the shaft.

That also means it must never be used as the locating bearing. It cannot position the shaft, and a shaft with toroidal bearings at both ends is axially undefined - it will float, which is a fault rather than a feature.

Typical arrangements pair a toroidal bearing at the non-locating end with a spherical roller or deep groove ball bearing locating the other, chosen for the thrust present.

Angular misalignment comparable to a spherical roller bearing, plus substantial axial travel - with both figures published for each size.

The concave raceway geometry allows the roller set to tilt relative to the rings, so housing misalignment and shaft deflection under load are both accommodated without edge loading the rollers.

Axial displacement capability is generous and scales with bearing size. Importantly, the permitted displacement is measured from the bearing's centred position, so the arrangement should be set up with the bearing near centre at ambient temperature, leaving travel available in both directions.

That setup step is easy to overlook. A bearing installed at one extreme of its travel has full capability in one direction and none in the other, and on a shaft that both grows and contracts it will reach its limit.

Both figures reduce somewhat under high load, so read them from the manufacturer's data at the actual load.

Long, hot or heavily loaded shafts where both misalignment and expansion are present.

Large fans and blowers are a classic case: the shaft is long, it runs warm, and the two pedestals are separately mounted so perfect alignment is unrealistic. Conveyor pulleys, particularly on long or heavily loaded belts, are another - with the added factor that a loaded pulley shaft deflects.

Other typical uses are mill and paper machine rolls, drying cylinders, crushers and vibrating machinery, kiln and dryer supports, and large pump and gearbox shafts.

The common thread is that the alternative - a spherical roller bearing with a sliding outer ring fit - has a history of sticking in exactly these environments, where the housings are dusty, damp or hot.

They are less relevant on short, cool, well-aligned shafts, where a simpler bearing arrangement is cheaper and entirely adequate.

Normal roller bearing lubrication, but particular attention to setting the axial position at installation.

Lubrication follows standard practice for large roller bearings - grease or oil selected for speed, load and temperature, with relubrication intervals from the manufacturer's data. Because these bearings often sit in hot or contaminated environments, the sealing arrangement usually deserves as much thought as the lubricant itself.

The distinctive requirement is axial setting. The bearing should be positioned so the rollers sit near the centre of their axial travel under normal running conditions, which means allowing for the fact that the shaft will be longer when hot than when the bearing was fitted cold. Manufacturers give a setting procedure and an offset for this.

Both rings can normally be fitted with interference, which is one of the advantages - but that also means the axial position cannot correct itself later, so the setting must be right at installation.