Abstract: A two-piece plastic fastener has a sleeve-like body comprising forwardly projecting flexible legs and having a concentric radially enlarged head at its rear end. Longitudinal slots in the body define the legs and space them apart laterally. A cylindrical plunger, forwardly insertable in the body to an operative position at which it holds the legs forwardly diverged, has two radially outwardly opening circumferential grooves, one near its front end, the other near its rear end. At the rear end of each slot in the body is a detent lug that has its rear end integrally connected with the body to have its front end flexible radially outwardly. These lugs detent-wise engage in the front groove to define a projecting position of the plunger and in the rear groove to define its operative position. Lugs and grooves are so configured as to offer more resistance to rearward than to forward plunger displacement.