Plugs for plugging holes in manhole covers

Claim 1

A ONE PIECE PLUG FOR CLOSING A HOLE IN A MANHOLE COVER HAVING TOP AND BOTTOM SURFACES, WHICH HOLE HAS A SMALLER OPENING AT THE TOP SURFACE OF THE COVER THAN AT ITS BOTTOM SURFACE, SAID HOLE HAVING A SHAPE OF A TRUNCATED CONE AND PROVIDING A CIRCULAR LIP AT THE TOP SURFACE OF SAID COVER; WHICH PLUG COMPRISES A SUBSTANTIALLY FLAT CAP MEMBER HAVING AN ANNULAR FLANGE PORTION AT ITS PERIPHERY, WHICH FLANGE PORTION HAS A BOTTOM SURFACE ENGAGEABLE WITH THE TOP SURFACE OF SAID COVER AROUND SAID LIP; A POST HAVING A LOWER END AND AN UPPER END DEPENDING FROM THE UNDERSIDE OF SAID CAP MEMBER, SAID POST BEING OF A SIZE PERMITTING ITS PASSAGE DOWNWARDLY THROUGH SAID CIRCULAR LIP; A PLURALITY OF CIRCUMFERENTIALLY SPACED, VERTICAL DISPOSED BUTTRESS FINSS EXTENDING RADIALLY OUTWARD FROM SAID POST, SAID FINS HAVING RADIALLY EXTENDING PORTIONS, THE EXTREMITIES OF WHICH LIE IN A CIRCLE HAVING A DIAMTER GREATER THAN THE DIAMETER OF SAID LIP; SAID POST AT ITS UPPER END HAVING A PERIPHERY WHICH PROVIDES A GRIPPING ACTION BETWEEN SAID POST AND THE LIP OF SAID HOLE WHEN SAID PLUG IS PLACED IN SAID HOLE WITH THE BOTTOM SURFACE OF SAID FLANGE IN ENGAGEMENT WITH THE UPPER SURFACE OF SAID COVER.