The hacksaw will often damage the last thread when it cuts. Running a nut off the end will fix this. You'll have to run the nut all the way down from the other end. This doesn't take long, if you chuck up the rod in your drill and let it do the work. Hold the rod vertically, with the drill pointing down, and just hold on to the nut enough to keep it from spinning.
While a strict figure for the bench’s weight capacity is not available, a quick browse through their other stand and bench products shows a general weight capacity well above most other brands. As such, while we cannot say for certain that this bench provides the best weight capacity, it is more than likely that it the capacity is similar to the other products in the catalog.