Fork oil grade

[BUNNERS]

Morning all
Can someone please advise the fork oil grade for my 1949 B31 I have looked in the service sheets
And can find the quantity but not the grade.

Thanks
BUNNERS

[Kernowpete2]

For my 1953 plunger model it says SAE50 in the summer. Same as the engine.

[BUNNERS]

Thanks for the swift reply