Backing Plate 6.5"W x 5"H for 1/2 hardware (5/8" hole size) You will need one for each side of the hinge.
Each HitcHinge needs two backing plates. They are sold in sets of 2 @$30.00 a set. Example you would need two sets of backing plates for two HitcHinges. This would give you 4 backing plates.