UltimateAddons 3 prong adapter plate with 4 hole Amps connector has been designed to allow users to use their existing 4 hole AMPS layout (30x38mm size between holes) mounting attachments with any of the UltimateAddons holders & cases which are fitted with the unique 3 prong patented design. The adapter plate simply screws into the 4 hole amps plate and had 3 prongs on the opposite side, allowing the user to attach the UltimateAddons case / holder.