I have a Circle Cutter Jig from my old "RotoZip - Rev01, Type 1" (which has long since died)

Old RotoZip - Rev01, Type 1 (Old Mounting System) w/ Circle Cutter Jig (CRCT1) & 90 Degree Attachment Tool (Zip Mate)

New RotoZip - SS355 (No mounting system, Just a foot to set the depth)

This nut will allow you to attach the "Circle Cutter Jig"