IMO, smaller than 1/4 shank and you will bend them pretty easy when you lean on them. HF won’t take that back so you can get something bigger than a dremel???
I tried the Fordham when I started gunsmithing because that was all the rage. Luckily, there was another gunsmith about a mile from me who let me try his. Didn’t work for me. But...you have to use what works best for YOU and not anyone else.
You could try some 5/32 shank burrs...I don’t think I’ve ever even looked for them.
