What tool is used to establish corners with courses marked and a line attached?

The tool specifically designed for establishing corners in masonry is the corner pole. This tool allows masons to accurately set the corners of a structure with the courses marked and a line attached. By using a corner pole, the mason can ensure that the walls are square and that the dimensions are precisely followed throughout the work.

Corner poles are typically longer and provide a stable reference from which to work, making it easier to visualize the placement of the materials and the alignment of the courses. This is crucial for maintaining the intended structure's integrity and aesthetics.

While other tools listed, such as the spirit level, chalk line, and measuring tape, are essential in masonry work for various tasks—like checking for levelness, marking straight lines, and measuring distances—they do not serve the specific purpose of establishing and securing corners in the same way that a corner pole does.