May I know if there is a weight restriction on the plank walk? If the harnesses were meant for americans?

No weight restriction, everyone can walk this trail. The Huashan Plank Walk is world's most dangerous hike, it is not very wide, one misstep and you fall 2155m. Complete focus is very important! To keep safety, before you walk on the plank walk, you are given a little harness to wear with two hooks to attach to the chains, it is not only for americans, but for everyone.