The NGK iridium "race" plug for use with high powered Mazda rotary combinations. Available in 10.5, 11, and 11.5 heat ranges. We have had great success with the 10.5 plugs on daily driven applications and generally recommend this plug up to the 500 whp range. For serious performance applications beyond that level, the 11 and 11.5 are available. Price is for a set of four spark plugs. Note: 10.5 and 11.5 heat ranges are kept in stock. 11 heat range is available by special order.