Most used welding table clamp is a modified bar clamp that uses a 5/8” bolt to table top. Can be used as regular clamp or spreader still. Secures 4” machinists vise horizontally or vertically to the table as needed. Good ground thru the table.
OK, here is one with Mr vice attached. What you can not see is the square tube for the vice plate is mounted 2" off of center. It that called non-concentric? What-ever-the-case, you can reverse it and the vice will then be over the edge by 2".