Hardened 52100 Spherical Plain Bearings are reviewed from a material and lubrication point of view for use in the off-highway environment. Abrasion resistance is excellent. Test results on Spherical Plain Bearings indicate that a coefficient of wear K of 1 to 3x10-8 for lubricated 52100 is consistent with experimental results reported in the wear literature. The Fundamental Wear Equation is applied with a K value of 2x10-8 to estimate the life of 52100 Spherical Plain Bearings in the absence of abrasion. Wear Coefficients from the literature are either unlubricated or continuously lubricated wear. The critical factor in applying a wear life equation under conditions of periodic lubrication is the life of a film of grease (lubrication interval), which is given here based on RBC Spherical Plain Bearing tests.