{TAIL ~ The guide arm} has a mount for fitting said machine tool and said housing has {HEAD ~ at least one top track wheel}, at least one side track wheel and at least one oblique track wheel adapted for rolling along the top, side and edge of the elongate track, respectively 
{ TAIL ~ The guide arm } has a mount for fitting said machine tool and said housing has { HEAD ~ at least one top track wheel } , at least one side track wheel and at least one oblique track wheel adapted for rolling along the top , side and edge of the elongate track , respectively
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH