The meaning of the English names of various bearings

NU——Cylindrical roller bearing with double ribs on the outer ring and no ribs on the inner ring NUP——Cylinder roller bearing with double ribs on the outer ring and single ribs on the inner ring and with a flat retaining ring Bearing RN——No outer ring cylindrical roller bearing NNU——It has the same meaning as NU, the difference is that it is double row NJ——Cylinder roller with double rib on the outer ring bearing