The PROdrive Stainless Steel Screw from Peak Design is a D-ring that screws directly into your camera's bottom mount. It allows you to use a variety of sling-style straps. A rubber pad acts as a protective buffer between the screw and your camera body while also preventing your camera from twisting while in use. The D-ring indexes in three positions so that it can lay flat against the rubber pad on either side of the screw, or in the middle when it is being used with a strap. A 4mm hex wrench is included to securely install the screw to your camera.