The igniter 2 wherein {HEAD ~ said gap filler} has {TAIL ~ a relative permeability} of not greater than 15 
The igniter 2 wherein { HEAD ~ said gap filler } has { TAIL ~ a relative permeability } of not greater than 15
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH