7 NOS CHAMPION Spark Ceramic Plugs For Various Radial Engines #C275S - Mainly Aircraft Thread Size & Series / Type Designator - Location. 18-1.5MM Base , 5/8 -24 UNEF Shielding . Electrode Style B11 Four Gap Ground Electrode .All Other Specs Can Be Goggled . Only One Opened For Photos . Selling As Seen - No Returns & FAST FREE SHIPPING