Hold Down Clamps for Harbor Freight Drill Press

I needed to clamp down a piece of aluminum on the drill press table.  (It was too big to fit in the drill press vise.). The drill press vise is held in place by a careless (or thoughtless?) combination of bolt two washers and a nut at the bottom.  These slide into what I would call the world's most sloppy T-slot.  Maybe this has a different name in this application.  Putting two of these in place holds the drill press vise in position just fine.  But these really do not work for holding a 5/16" aluminum plate.  

The slots are 1.09" wide where the threaded T-nut should go and .5" deep.  I cannot find anything that fits this description or associated with Harbor Freight. 

Because the measurements are a bit difficult inside a T-slot, making my own T-nuts for this  makes a lot of sense.  If they turn out too wide or too high to slide, I can just machine them a bit narrower or shorter.  I need to make them of steel.  They should be much easier to install than the current expedient solution.  By attaching a sheet of steel under the top of bolt, I should be able to clamp stuff to the drill press table.

I am blogging this because I have a bit too much to do on the gun rights front right now, and if I write down these dimensions I am guaranteed to lose the paper by the time I am ready to machine these.