From Manufacturer
The Professional Series USA Gear Dual Grip Hand Support and Wrist Strap from Accessory Power is a combination wrist and hand support for most DSLR cameras. It is compatible with cameras that have a 3/8" neck strap webbing connector and 1/4-20 tripod mount.
This system provides you with two connection points that prevent your camera from slipping out of your hand. First, thread and secure the grip strap's webbing through your camera's neck strap lug. Second, attach the tripod connector to the 1/4-20 tripod socket of your camera. The tripod connector features an additional female socket to connect your camera to a tripod or monopod. Finally, wrap the neoprene support around your wrist and secure it via the touch fastener. This support stretches to accommodate wrist sizes of 4 to 10.5". This still allows you to maintain full control of the camera and guards against incidental slips while providing additional shooting stability. Your camera is now held at two points and remains firmly in your hand in shooting position.