If “Object Effectivity” of the Primary Info. tab is selected as :

Parts - The system lists only “Parts” in the “Obj. Eff. Ref.” drop down list box

Aircraft - The system lists only “Aircraft” in the “Obj. Eff. Ref.” drop down list box

Both - The system lists “Part”, “Aircraft” and “All” “Obj. Eff. Ref.” drop down list box)