A fastener for mounting a panel to a supporting structure includes a fastener part having a base with an upper and lower side. A connector is adapted to engage with another fastener part projecting from the upper side of the base. The lower side of the base is adapted to be adhesively connected to a substrate and incorporating a surface configuration that promotes a mechanical connection with an adhesive. The lower side surface configuration includes a protrusion extending from the base to a crown. The protrusion includes an undercut portion configured to form a mechanical connection with the adhesive. In use adhesive fills between the protrusions and forms a mechanical connection with the undercut portions when hardened.