Harden or not…use cap heads/grub screws..hard before you start…
It can also be argued to use over size screws and leave soft..but reduce contact point to avoid removal probs.

I usually stick a shim ofscrap ally between the bolts and the tool to avoid marking it. And I think the bolts have the threads turned away slightly so if they do get mushroomed, they can still be unscrewed from the holder.

W.

One word of caution regarding fasteners, whilst the imported and economical Allen screws are probably good enough for some applications they are no where near the strength and quality of say Unbrako fasteners.

I bought a selection of imported ones from J & L one MSC and they are OK , I have used them for many jobs but they are next two useless as replacements in my Dickson tool holders so I purchased Unbrako for these.

Just my observations and thoughts.

John