The square seat bracket is the most commonly used basic clamping equipment in middle school physics laboratories, used to clamp glass instruments such as test tubes, flasks, funnels, burettes, asbestos nets, etc., ensuring experimental safety, accuracy, and repeatability. Experimental application example: Combination of fixed pulley/movable pulley to verify the decomposition and synthesis of force. Electrical experiment: Clamp conductive rods and metal sheets to build a simple circuit. Thermal experiment: Place asbestos mesh on an iron ring and heat the water in the beaker with an alcohol lamp. Chemical experiment: Titration analysis, fix the burette with parallel clamps, and place the conical flask with an iron ring. Sensor Expansion: The upright pole can fix displacement, temperature, and photoelectric sensors to achieve digital experiments.