QA1's MIB and MIB - T Low Carbon Steel Series spherical bearings offer more wear surface than a traditional COM bearing, extending the life due to the increased race width and diameter. An optional self - lubricating PTFE liner is also available with these spherical bearings (MIB - T Series). BALL, 52100 Bearing Steel, Heat Treated, Hard Chrome Plated, Precision Ground, , LINER (MIB - T), PTFE, Self - Lubricating, , RACE, Low Carbon Steel, I.D. Protective Coated for Corrosion Resistance, Oil Coated, Mfr.'s Option - Heat Treated Stainless Steel.