Base jacks are normally fitted at the bottom of the legs of scaffolding in the building trade, in order to provide stability, and to level the equipment on to the ground. They are also widely used in boatyards, as  supports, when the boats are not in the water. They have a a steel base plate with four holes, which can take screws in them. Threaded bars, of various lengths are welded on to the base, and an adjustable fly nut provides the right setting.