Double-sided panel connectors, also known as 'back-to-back' or 'bulkhead through-adapters'. These have N connectors on both sides of the panel. Single hole fixing type, or square flange type with four screw fixings. Panel hole diameter 16.0mm for single hole type, 16.7mm for square flange type. Fixing centres 18.2mm x 18.2mm for square flange type.