i don't know for sure but i would assume the held some kind of table leg socket at one time from the looks of the screw pattern look and see if there are any circular marks around the screw pattern that may indicate a flange of some sort was there
They are the remnants of the table base socket. Oday had an aluminum base socket on the 20 and 22 that a stainless tube fit into and a table approximately 18 X 18 inch with another socket that provided a reasonable table that could be stowed away until needed. Of course this left the base in a lovely position to trip over. Probably why you have only the screws remaining.