My old bench had a vise that would rack, so I cut out several pieces of 4″ X 1 1/2″ x 1/4″ popular that I had lying around and drilled a 3/4″ hole (you may have to sand the holes or the dowel little bit to get the pieces to rotate easily) in all of them and inserted a 3/4″ dowel with 2 scrap turned end pieces screwed and glued and presto a variable anti-rack block, It can go from 1/” to 2″. This is not an original idea, I have seen wooden versions of similar rack stops on the internet and there is a plastic version of this in a Lee Valley catalog. It’s just really easy to make and works great!

Peace