Clay based grease, thickened with bentonite clay rather than a metal soap, has one defining property: it has no dropping point. The thickener does not melt, so the grease will not liquefy and run out of a bearing at high temperature.

That makes it the answer for kiln trolleys, oven and furnace conveyors, foundry equipment, drying plant and other bearings running at sustained high temperature where a lithium or calcium grease would simply flow away.

The practical limit is the base oil rather than the thickener. The oil eventually oxidises off and leaves the clay behind as a dry residue, so relubrication needs to be frequent and generous rather than on long intervals. Clay-based grease is generally not compatible with lithium or calcium products, so purge bearings thoroughly when changing over.