Brisk Racing Silver plugs rated 3 to 4 steps colder than stock. For 6.1L / 5.7L HEMI. We recommend these plugs for all forced induction and nitrous applications from 800 to 1000 RWHP cars. Sold as a set of 16. BRISK Silver Racing RR12S Spark Plug 14mm thread, 25mm reach, 5/8'(16mm) hex, tapered seat, non-projected tip, resistor, fine wire 1.5mm Silver center, Cut-back ground electrode. Brisk Silver Racing plugs have a better ignitability than conventional performance spark plugs, and offer better performance and reliability in high boost, nitrous or high compression applications. Silver is an element with the most free electrons, and is the best electrical and thermal (heat) conductor of all metals! Better than gold, copper ...and many times better than Iridium. The Brisk Silver Racing plugs have a fine wire center electrode (not just the tip), which gives more room for insulator between the center electrode and spark plug shell. More insulation results in a durable spark plug with high dielectric strength - the most important spark plug parameter in forced induction applications. In street applications, the greatest advantage is a powerful spark, improved performance, low ignition voltage requirements, excellent heat dissipation at full load and excellent anti-fouling resistance under light load operation.