Tweco switchable magnetic ground clamps use a magnetic field to hold the ground to the work piece. They are easily switched from an on to off position by simply turning the knob on the top of the clamp. Clamps are perfect for use on flat, round or irregular shaped surfaces. Clamps can withstand temperatures up to 176° F (80° C) and still remain tough, strong and durable. This is a 300 amperage maximum ground clamp.