A tool for mounting a coreless roll of flexible sheet material on a replacement core apparatus including a replacement core and an insertion aid having a polygonal outer end and a base having a profile that matches the profile of outer surface of the replacement core, the replacement core in an embodiment having an enlarged lip member on at least one end, whereby the insertion aid is dimensioned such that it fits over the enlarged lip member enabling the replacement core to be inserted into a central aperture of a coreless roll with the end having the enlarged lip member passing through the center aperture, and in another embodiment the insertion aid having a crenulated tapered section that transitions the outer surface from a polygonal shape to a circular shape to match the cross section of the at least one lip member or outer surface of the replacement core.