This is a 5/8" to 3/4" hose mender coupler by Gilmour.
The coupler is constructed out of thick nylon and features screws that can be adjusted to fit onto a variety of differently sized hoses.
It measures 2.1" in height, 1.5" in width, and 1" in depth.
This item appears unused and still features its original tags, but is slightly discolored.