This is an ABS trigger ring that is used on the VR4/TT front halfshafts - they are just pressed onto the end of the shaft where it goes through the hub. They are no longer available from Mitsubishi but these aftermarket ones are exact replacements - and less $$ too!!
While they are for the AWD cars, they can also be used by FWD owners who are doing the VR4/TT brake conversion - installing VR4/TT front brakes onto their FWD 3000GT/Stealth. These rings simply hammer onto the ends of the FWD halfshafts. Of course, you will also need the VR4/TT ABS sensors to pair with these. Please see the Tech/FAQ article for details on the FWD-to-AWD brake conversion.