Vise Adapter - Round/Cylinder/Post Clamp
thingiverse
Really simple little parametric model (OpenSCAD file included) that will take your entered post diameter and make an adapter for that post to go into a vise. I used this to put a bicycle seatpost in a vise and get a firm grip without ovaling the post. Provided STL is 26.8mm because that's the post size I was working with. It will work with lots of objects, just change the post_diameter variable. Set your infill based on how much force you'll need to apply. If it's delicate work I'm sure you can get away with 5-10%. If you're going to wrench hard, you might want to consider 80-100%.
With this file you will be able to print Vise Adapter - Round/Cylinder/Post Clamp with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Vise Adapter - Round/Cylinder/Post Clamp.