This old pre-1900 cast-iron pair were meant to hold or lock the sash into a fixed position–or to stay the window in an open position or locked position. One stay is screwed to the left and right edge of the window close enough to allow the base to press up against the frame–which fixes the window into a stationary position.
The banjo has a pinwheel pattern. There is a patent date stamped on the back that looks like “Aug. 28, 85.” The hole centers, for the stay that screws to the window, are 1 1/2 inches apart. The base, that pushes against the frame, is 1 1/2 inches long and 1/4 inch wide. The arm or lever projects 1 1/4 inches. When this arm is engaged, the base is pushed into the frame.
Screws will be included.