This Alternative 5 way Girling type brake union has 3/8th UNF threads to all openings so you cannot use the original Isetta Girling brake light switch which is why its comes complete with a switch. The openings have a concave seating which is different to  the original union so must use Universal Brake Pipe Flairs. It is compatible with the Automecs Brake Kits we sell.   If using your own flaring tool use step number one only