Hydraulic hose

What are the compatibility rules for all the hoses, banjos and bolts used to make up a hydraulic hose?
I seem to be buying components and then discovering that they don't fit together. I feel a bit stupid, but not so stupid that I can't ask for advice.
I seem to be buying components and then discovering that they don't fit together. I feel a bit stupid, but not so stupid that I can't ask for advice.