Roller body, method of its manufacture, and of roller or plain bearings

A roller body for a bearing, said body comprising a core of ceramic material consisting essentially of silicon nitride (Si.sub.3 N.sub.4) with a density of less than 6.5 and a hardness of at least 1000 Vickers, said core having a surface quality Ra of 0.1 to 1.0 .mu.m, and a roundness of 0.1 to 1.0 .mu.m, said body further comprising an outer coating comprising titanium nitride (TiN), the coating's surface having a quality Ra of less than 0.025 .mu.m.