Lightning direct effects threats are a major concern for aircraft manufacturers. Of particular concern are fuel ignition threats caused by lightning current transfer between metallic fasteners and surrounding structures leading to voltage arcs, thermal sparks and pressurized gas effects. Although a large percentage of a modern aircraft structure is being replaced by carbon fibre reinforced plastic (CFRP), the main structural components remained joined by means of bolted joints. Although particular choices of fastener technologies are known to affect the current threshold for initiating arcs and sparks, the contributing effects of each design parameter of a structural joint are still not fully understood due to the fact that exploration of these parameters is primarily assessed using measurements. This paper reports a realistic model of a structural joint that includes the metallic bracket (representing a structural spar or rib) joined to the CFRP layer using a detailed model of a fastener (washer, nuts and bolts). The model is simulated using a robust broadband time-domain numerical model based on tetrahedral meshes. The design parameters of the structural joint are explored when high currents are directly injected into the fastener on a metallic bracket.