I prefer square shanked hardy tools since I also use them in my fly press and vice and square is simple. Most of my hardy tools have quite short shanks. I have a broken heal on my anvil, so made my own solid bolster for hardy tools. The bolster is a 2" thick slab welded on 4 upright 3" bars about 10" long. To make the square hole, I drilled a bunch of small holes and then chiseled it out. At 5", you have a much thicker piece of stock, but if you run hardies with a small shank, there is no need to chisel a square hole all the way through.