This is the large single ball bearing that was fitted on the top vertical bevel gear housing on the SOHC Walter Moore CS1 or CSJ engine, manufactured from 1927 - 30. This is a high quality SKF brand bearing.
The second picture of this listing shows the Norton Spare Parts List for the 1927-30 CS1 Model, showing the bearing listed here - as Part No 4130.
This bearing is a high quality SKF bearing.
If you have a requirement for other bearings to fit CS1/CSJ or other 1920's Norton models - we may be able to obtain them - email us at email@example.com