M/cycle puzzle
 

I found these Motorcycle parts books at a swap meet.

The books have a military connection: SWPA HQ 1942 . Printed in Melbourne.

Interesting that the book shown is for 1937 models only and says to refer to separate books for 1938 and 1939 models. This suggests that all three model years were acquired at the same time as normally the 1938 and 1939 would refer to previous years but not 1937 to future years. Otherwise, the way it is worded suggests they knew that they would be purchasing more in future and that they would be different... hardly what you want for ease of maintenance.

They were printed in 1942, I understand from Mike’s message, in which case it makes sense to have a book for the 1937 model refer to other books for later models.