I designed this because I needed to cut down a metal rod for a 3D print project. Of course didn't want to damage the rod in a flat vise so I came up with this adapter. Designed with Fusion 360 and a high angled cut-out to hopefully allow various sizes without any issues. Print with so small sides are up and down. I think the weak spot would be at layers and a rod would push them apart under pressure if layers are running parallel to rod, so printing with layers perpendicular to the rod in a vise seem to make sense and keep strength. If too long for your vise just scale height only in your slicer down to what is needed. Will have to make two of them as well.

I used Cura .2 profile and 50% infill, maybe a bit overkill with the infill but seemed like it wasn't a terrible idea either due to the stress.