A strong vise base
When I built my garage/shop, I set a 16" length of 2 1/2" sqare tube with rebar welded to it in the floor and poured the cocrete around it. I have a length of 2" sqare tube I drop in it and a short piece of 2 1/2" square tube welded to the vise base to drop over the 2". It's plenty strong. While repairing some front end damage on my grandson's car, I had to pull on it with my 1 ton cable hoist and had the tires sliding on the floor. When the vise isn't needed I pull the tubing out of the floor and plug the hole with a piece of foam rubber.