These two properties are used to identify the maximum number of objects that can participate at each end of the relationship. The most common values are 1 or *.
A relationship configured with Max2=1 means that the object at end 1 can only be related to a single object at end 2. For example, SPFDocRevisionLabel is configured with Max2=1 because a document revision can only have one label.
A relationship configured with Max1=1 means that the object at end 2 can be related to only one object at end 1. For example, SPFMenuItems is configured like this because a menu item can only exist on one menu, but a menu can have many menu items.