Bearings are shielded to prevent penetration of dust and grease packed for life.
They should not be cleaned with solvent or lubricated as this will dissolve the grease and cause premature bearing failure.
Scrape off any resin build-up.
Always check the tightness of the fixing screw before using cutter.

Specification:
OD=21 mm
ID=3/16 inch
Thickness=6 mm