18 X 1.5 THREADED BUNG "WITH 30` TAPER" AND PLUG KIT.18 X 1.5 BUNG IS 1018 mild STEEL, PLUG IS STAINLESS STEEL. THESE WILL LET YOU PUT YOUR O2 SENSOR IN MANY PLACES WHERE A STRAIGHT FITTING WILL NOT WORK. MADE IN USA NOT A CHEAP IMPORT. HEX ON THE PLUG IS 1 INCH. CHECK OUR OTHER LISTING FOR MORE BUNGS AND PLUGS, We make many different styles of bungs. We recommend that you apply a small amount of anti-seize to the threads of the plug before installation. PLUG IS NOW STAINLESS STEEL to resist rust !!!!!!