A one piece push-in fastener for insertion through a hole includes a head, and an elongate shank extending from the head and terminating in a tip. The fastener also includes a shoulder spaced from the head and extending radially outward from the shank, and a plurality of spaced ribs extending radially outward from the shank and disposed along a length of the shank between the shoulder and the tip. A diameter of the head is greater than a diameter of the shoulder.