Solid cast brass Square Shutter Dog Post for windows/shutters. Lightly textured, traditionally cast. Used to support shutter dogs. Several finishes available. In engineering, a dog is a tool or part of a tool that prevents movement or imparts movement by offering physical obstruction or engagement of some kind. It may hold another object in place by blocking it, clamping it, or otherwise obstructing its movement. So a "Shutter Dog" is a stay that holds a shutter in place. These are traditionally used on the exterior of a house to hold a shutter open. They are historically found in a variety of shapes including grapes, shells, "S" shapes, and "rat-tails" among others.