The Black Widow Pin from Spider Camera Holster is part of the Black Widow System. This pin screws into your camera's tripod mount and then slides into the the Black Widow Holster. Made from solid steel, it provides support for the camera and pivots along with your body as you walk.
I screw and Loctite these into Universal Aluminum Arca Swiss clamps from everyone's favorite online general store to make light and inexpensive Spider Holster pin to Arca plate adapters. I put them on all my Arca-plated cameras, and carry them on a Spider Pro belt at my waist. This keeps the camera and lens weight off my neck, lower back and shoulders - no neck-strapped cameras for me. It also lets me quickly grab a camera for shooting. The resulting adapters are easy to remove when I want to tripod-mount a camera.
I ordered this pin to use with a spider x holster for a low profile belt carry and it works perfectly. The picture needs to be updated as it shows the old version of the pin but you do actually get the new design with the flattish ball and the little hole through the side of the hex nut part.