Ⅰ: Code of product series: three-digit

      131: series 131 4D module

Ⅱ: Sequence number of RD: single-digit

      1: generation 1

      2: generation 2 (external encoder, V type)

      3: generation 3 (internal encoder)

      5: generation 5

Ⅲ: Code of matched encoder: single-digit

      0: without encoder    

      1: 1232210306500  2: 1232010306500

      3: 1230020406500  4: 1232010406520

Ⅳ: Code of left and right switch: single-digit

      0: without switch    1: 1580360740100

Ⅴ: Code of central switch: single-digit

      0: without switch

      1: 1580550740100   2: 1580360740100

Ⅵ: Color of rubber wheel: double-digit

      00: black     01: gray     02: red

Ⅶ: OD of rubber wheel: double-digit

      22: φ22     24: φ24     26: φ26

Ⅷ: Derivative code: single-digit

      0: without special items

Ⅸ: Type of package: single-digit

      0=plastic bag         1=shrinked plastic package

      2=tape package     3=tube package  

      4=foam package    5=undetermined