Abstract: A method and means is provided for securing the bottom closure of a polygonal container having a plurality of side panels and a strong weight supporting bottom formed by a plurality of generally triangular bottom panels and a plurality of interconnecting webs between the panels. The method comprises inserting a fin head assembly within the container, the fin head assembly having a plurality of vertically disposed fin plates which are registered in alignment with the junctures between the side edges of the bottom panels. The fin plates are then inserted into the junctures between the side edges of the bottom panels so that each fin plate is embraced between the double thickness of the web panels which are between the side edges of the bottom panels. The fin plates hold the bottom panels and webs in place so that a clip may be placed over the circular array of ribs formed by the double thickness web panels, thereby holding the web panels and the bottom panels in a predetermined configuration.