Necks
 

Are fender precision bass necks the same as Jazz bass necks.Interchangeable and fit the bodies of both?

They should be interchangeable, but not the same. Jazz necks typically have a slimmer profile, with less meat on the back of the neck, but unless you are using different brands of necks they should have the same mounting area, so you can easily put a jazz neck on a P (commonly done) or vice versa (less commonly done). Even if there is a slight difference, it should be small enough to be corrected with a bit of sanding.