Abstract: A two part fastener is provided for securing an elastomeric membrane on a roof deck or the like. The fastener includes a post secured to the roof deck by a screw and having a peripheral laterally extending flange at the upper edge. The membrane is draped over the post and a ring is installed over the membrane and post. The ring includes a plurality of inwardly and upwardly directed resilient fingers lying on a conical surface. The fingers snap over and then lock beneath the membrane and flange. The upper end of the post is recessed so that part of the membrane can be stretched into it during assembly and then released to reduce stress in the membrane.