Shimano locking disc for Nexus hub blue.

Fit:

SG-5R30

SG-5R35

SG-8R20

SG-8R22

SG-8R25

SG-8R27

SG-8R30

SG-8R31

SG-8R35

SG-8R36

SG-C6010

SG-C6060

SG-S500

SG-S501

SG-S700

SG-S7000

SG-S705

WH-8R25

WH-S500

The marked part, # 23, on the picture.