The oldest clawfoot tubs appeared in the 1880s. John Kohler advertised his as industrial horse trough that would convert to a bathtub when feet were added. Other companies had their own models, offering several different style of feet. The four most common were the cannonball, the paw, the armada and the ball and claw. Cannonballs are simply round feet with a flat spot where they would sit even on the floor. Paws look like cat or dog paws. Armada are geometrical blocks, either square or rectangular. The ball and claw style places the ball below the claw, which appears to be grasping it.
Like the styles of antique feet, their attachments varied wildly. Each company's tub was keyed specifically to its foot, which is what makes replacing them today so difficult. Some tubs relied on a level style attachment, where the foot slipped into a tab and was held on by the weight of the tub. Others had built-on clamps that were screwed on to a corresponding lip. Another style featured a long stub piece that slid into a cast pocket.
Modern clawfoot tubs also run the gambit in foot style, but they have a great deal more in common. The heavier iron tubs have feet that bolt on through holes that are drilled through the outer wall of the underside of the tub. Some fit over a bolt and are tightened down with lock nuts. Others fit onto elongated straps that better distribute weight across the feet and floor below.
Universal strap systems exist to replace missing feet or to add a little more stability to clawfoot tubs on uneven floors. These systems look a lot like a bed frame. Each foot has a metal support that attaches between it and the next foot, forming a square. The metal supports are designed to be screwed to a tub with screws, but the weight of the tub also helps to stabilize the system.