I'm setting up a milling table which uses 9/16" T-nuts. The problem is that one tool I want to attach is a vise with smaller feet, somewhere between 1/4" to 3/8". I just wondered if there were such things as threaded sleeves so that a smaller bolt could be able to go into the larger nut. Is there some such thing at a place like McMaster Carr and what is it called?

Steve