Abstract: A fastening element for a joint forming device includes an elongate dowel and a sleeve for the dowel. The dowel has a head portion at one end thereof which is engagable in use with a tightening element. The dowel is adapted at the other end thereof to co-operate with the sleeve to cause radial expansion of an expandable end section of the sleeve upon relative axial movement between the sleeve and dowel. The expandable end section of the sleeve is insertable axially into a mounting hole in a first panel. The head of the dowel is insertable axially into a mounting hole in a second panel whereby to enable engagement with said tightening element. The sleeve is configured to allow the position of the dowel within its mounting hole in the second panel to be adjusted to enable insertion of the expandable end section of the sleeve into its mounting hole in the first panel, in use, even if the axes of the two mounting holes are out of axial alignment.