"6" indicates deep groove ball bearing (Class 0)

"4" indicates double row deep groove ball bearing (Class 0)

"2" or "1" refers to self-aligning ball bearing (four numbers in basic model) (type 1)

"21", "22", "23" and "24" refer to self-aligning roller bearings. (Class 3)

"N" refers to cylindrical roller bearing (including part of short cylindrical roller and slender needle roller) (Class 2)

The "Nu" inner ring has no retaining edge.

Single stop edge of "NJ" inner ring.

"NF" outer ring single stop edge.

The "n" outer ring has no flange.

"NN" double row cylindrical roller, outer ring without flange.

"NNU" double row cylindrical roller, inner ring without flange.

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

"Na" spinning outer ring needle roller bearing

"NK" stamped housing needle roller bearing

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

"7" indicates angular contact ball bearing (Category 6)

"3" indicates tapered roller bearing (Metric) (category 7)

"51", "52" and "53" refer to radial thrust ball bearing (five numbers in total for basic model) (category 8)

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

"29" indicates thrust self-aligning roller bearing (Class 9)