jack stand

A jack stand exists because a jack is not a support. The jack's job is to lift the car; the stand's job is to hold it there. Once the car is up, a pair of stands is placed under the points built to take the load — the frame rails or the manufacturer's jacking points — and the jack is lowered until the weight rests on the stands.

The failure it prevents is quiet. A hydraulic jack can bleed down over hours, and a car resting on a jack alone can come down on whoever is beneath it, which is why the rule is absolute: no part of a body under a car held by a jack, ever. The jack is left in place as a backup under the raised corner, wheels are chocked so the car cannot roll, and the work happens on firm, level ground rather than dirt or asphalt softened by the sun.

Stands are rated in pairs by capacity, and substitutes are not substitutes: a cinder block, a stack of bricks or a length of firewood can crumble or shift under a load a rated stand is built for.