For use on hard or abrasive surfaces such as concrete or vinyl the 3 legged thing heelz provide extra stability to your tripod they are made from premium stainless steel and are designed to reinforce and protect your tripod and the camera equipment attached to it each one has a 14 20 thread and 38 stainless steel threaded sleeves so they are universally compatible with any tripod that has either of these standard fittings