Selecting the correct spark plug requires matching the Heat Range to the engine's operating temperature; a 'cold' plug is essential for high-performance engines to dissipate heat quickly, while a 'hot' plug prevents carbon fouling in low-speed city driving. You must also verify the Thread Diameter, Reach, and Hex Size to ensure a perfect mechanical fit. For modern vehicles, prioritize Iridium or Platinum-tipped electrodes as they offer superior conductivity and a lifespan of up to 100,000 miles, compared to standard copper cores.