Because of their square cross-section, staples make good stirrup steps. They aren't really suitable for handrails or grab irons, which are typically in the 3/4"<1" diameter round stock range.
I use a lot of paper clips in my modeling, in just about every available size. The smallest size I have, with the smallest diameter wire, is about 50mm in diameter in 1:80 scale, or over two inches in HO.
In my own work I've used magnet wire - and extreme care when handling the models so fitted.
Chuck (Modeling Central Japan in September, 1964)
Staples might be OK if the width is right, but they have a square profile whereas the prototypical grab rails were round. Any paper clips that I have seen are much larger in diameter than the 1" prototype diameter grabs (please correct me if I am wrong on the 1" prototype diameter).
I use Tichy phosphor bronze wire to make my own grab irons. Their .010" stock is close to prototypical size. http://www.tichytraingroup.com/index.php?page=view_category.php&category=Wire&offset=0
Bottom line is - you can use whatever you want, especially if the price is right. It is your railroad after all!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!