A fastener includes a cylinder and a draw hook. The cylinder includes a main body, two resilient arms extending from an end of the main body, and a flange extending from a circumference of an opposite end of the main body. A number of protrusions spaced in the axial direction of the main body extends from an inside surface of each of the resilient arms. The draw hook includes a post slidably received in the cylinder, a taper-shaped engaging portion extending from an end of the post and exposed out of distal ends of the resilient arms, and a handle extending from an opposite end of the post. A diameter of the engaging portion gradually grows larger along a direction away from the post.