• A blackboard set square, often referred to as a 45-degree set square or triangle, is a geometric drawing tool used in mathematics, drafting, and engineering to create and measure angles of 45 degrees.
• It's commonly made of transparent plastic or other durable materials. The set square is designed to assist in drawing accurate lines and angles on a blackboard or similar writing surface.
• The "45-degree" designation indicates that one of the angles within the set square is a right angle (90 degrees), and the other two angles are each 45 degrees.