Hs474dzb rail adapter

Recently imported the Japanease 125mm saw. Can anyone give me a part no for a compatable rail adapter that will work with it as my searching has come up short. I was wondering is there is a spefficic one as on the back edge of the base plate there is a grove and threaded holes that look like they would accept something but I am stumped and there is nothing in the manual that gives a ahit of something