The first number from left to right or the first and second numbers are added together

"6" means deep groove ball bearing (category 0)

"4" indicates double row deep groove ball bearings (category 0)

"2" or "1" indicates aligning ball bearings (basic model has four numbers in total) (Category 1)

“21”, “22”, “23” and “24” represent spherical roller bearings (category 3)

"N" indicates cylindrical roller bearings (including short cylindrical rollers and part of slender needle rollers) (category 2)

"NU" inner ring has no ribs

"NJ" inner ring single rib

"NF" outer ring single rib

"N" outer ring has no ribs

"NN" double row cylindrical roller, outer ring without ribs

"NNU" double row cylindrical roller, inner ring without ribs

The roller length is at least 5 times the diameter, which is called a needle roller bearing (category 4)

"NA" turned outer ring needle roller bearing

"NK" stamped housing needle roller bearings

"K" needle roller and cage assembly, without inner and outer rings

"7" means angular contact ball bearing (category 6)

"3" indicates tapered roller bearings (metric) (category 7)

“51”, “52” and “53” represent radial thrust ball bearings (the basic model has five numbers in total) (category 8)

"81" indicates thrust short cylindrical roller bearing (category 9)

“29” indicates thrust spherical roller bearing (category 9)