Abstract: A metal insert, especially a threaded insert, is secured in a lightweight, andwich type panel with the aid of a spreading dowel. First, a hole is machined, for example drilled, through one cover and through the core of the panel down to, but not through, the other cover. Then a spreading dowel is inserted into the hole so that it rests on the other cover. Then the metal insert is pressed into the spreading dowel, whereby the spreading wing elements are spread substantially radially outwardly until the outwardly facing surface of the insert is flush with the outer surface of the panel cover. In the last step the voids are filled with a hardening or curing synthetic resin bonding material. The spreading dowel has a leg base and spreading wings hinged to the base. A cam surface on each wing assures that the force resulting from pressing an insert into the dowel spreads the wings until the insert rests on a shoulder of each wing.