608-2RS Ball bearing.
The bearing is 8 mm ID, 22 mm OD, and 7 mm wide.
This bearing is the rear bearing in the motors of all mini mills and mini lathes.
Part # 155 on SC4 parts diagram (SC4-155)
These are NTN, Nachi, or equivalent brand, permanently lubricated and sealed bearings.
In your instruction manual, this part appears on the parts list as: