Primary Function: A jack's primary function is to lift a vehicle, but it is not designed to hold a heavy load for an extended period. Jack stands are designed specifically for this purpose. They are a "fail-safe" device, providing a reliable and solid support system that a hydraulic or screw jack cannot.
Construction: Jack stands are typically made from high-strength steel or aluminum, designed to hold significant weight. They feature a wide, stable base, often in a tripod or four-legged design, to prevent tipping.
Adjustable Height: Most jack stands have an adjustable column that can be raised or lowered to the desired height. This allows them to be used on a variety of vehicles, from small cars to large trucks.