A fastener may include an anchor that is configured to be inserted into an attaching hole formed in a panel. The anchor includes a pillar, at least one engagement strip positioned in at least one side of the pillar, and a guide block formed in a distal end of the pillar and having a planar shape corresponding to a shape of the attaching hole. The at least one engagement strip is capable of passing through the attaching hole while being flexed inwardly and engaging a periphery of the attaching hole when the anchor is inserted into the attaching hole. The guide block is configured to pass through the attaching hole only when an axis of the anchor is positioned substantially perpendicular to a surface of the panel.