Iridium and platinum technologies combine with Denso's 360-degree laser welding process to create a plug with a lifetime over 100, 000 miles. TT or Twin-Tip technology promotes spark energy concentration and explosion, which translates into improved acceleration and economy. Iridium TT feature the world's smallest 0. 4mm iridium center electrode and 0. 7mm needle tip ground electrode, which minimize spark interference and maximize ignitability, resulting in better power, torque and fuel economy. Denso's patented iridium alloy has the highest iridium concentration, making it more durable and producing a dramatic improvement in spark plug life