Counting from left to right the first or the first and second digits together

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

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

"2" or "1" means self-aligning ball bearings (four numbers in total for the basic model) (category 1)

"21", "22", "23" and "24" represent spherical roller bearings. (3 categories)

"N" indicates cylindrical roller bearings (including short cylindrical rollers and part of slender needle rollers) (Class 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, no rib on the outer ring.

"NNU" double row cylindrical rollers, inner ring without ribs.

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

"NA" Turning Cup Needle Roller Bearings

"NK" Stamped Case Needle Roller Bearings

"K" needle roller and cage assemblies, without inner and outer rings.

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

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

"51", "52" and "53" indicate radial thrust ball bearings (five numbers in total for the basic model) (8 categories)

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

"29" means thrust spherical roller bearing (category 9)