A Firewall Passthrough, custom made for application. Commonly used for wire harness / ECU connection to penetrate firewall.
The ECU Loom has a large plug permanently attached to the engine, which means you need to add a hole much larger than the actual cable loom to pass the plug through from the engine bay to the inside of the cabin (where you ECU is installed). Rather than have to patch up a larger hole using other improvised methods, you can use this beautifully made billet aluminium clam-shell system. You simply install the top and bottom halves each side of the cable and use the supplied silicone patches to seal up the slightly over-sized reveal left by the pass through.