BlackRapid Black Rapid Straps FastenR for R Series Straps.

FastenR...
The FastenR is the point of contact between the camera and the R-Strap. Made from aircraft aluminum with stainless steel threads, then powder-coated in black, it screws into the tripod socket located on the underside of the camera body or lens.

The lock nut is then tightened down to ensure that the FastenR doesn't inadvertently unscrew. If you're using a tripod plate with a d-ring, you may not need the FastenR.

Simply attach the R-Strap to the d-ring, and you'll be able to release the camera quickly from the strap for mounting on your tripod.