A screw down test clamp is a type of grounding hardware used in electrical systems to test the continuity and effectiveness of a grounding circuit. It typically consists of a metal clamp with a threaded bolt that can be tightened or loosened to make contact with a grounding conductor or rod. Screw down test clamps are designed to allow for easy and quick testing of a grounding system without the need for special equipment. They are commonly used in telecommunications, power distribution, and lightning protection systems to ensure proper grounding and safety of personnel and equipment.