Ordering a Rex gate hinge, is a simple procedure.  Generally there a two alternatives.  If it is a new installation, then a full set is necessary which includes a body assembly with angle brackets and all fittings. Order a Rex Gate Hinge Complete.
Rex
How to Order
Rex Series 3 Pivot Gate Hinge
If it is a replacement, then usually only a body assembly is necessary as all parts are interchangeable. Order a Rex Gate Hinge Body Assembly 
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There is a third option but this only applies to manufacturers.  Those who also make the gates and door assemblies to which the hinges are fitted.  Some prefer to weld the brackets to a steel post and powder coat the complete assembly as one. Order a Rex Gate Hinge  Unpainted