What is the acceptable drum thickness spec range for front and rear drums before they are not considered to be useable?

I'm more interested in F1 specs, but other models would help too for future reference.

I have several drums (F1-F3) and need to figure out if I should hold onto them or send to scrap.

Thanks.

 

It's in the Specs section of the manual

 

Duh! Why didn't I just look through the manual first?! Thanks for pointing out the obvious, Ross.

 

It is usually stamped on the drum what the tolerance should be.

 

Not back in the 40's/50's