> They may be a special form of pop-rivet.  These are much like 
> standard pop-rivets but the center mandrel is a hex shape.  This 
> creates the hex shaped hole down the center.
> 
> They are used exactly like a pop-rivet but are removable under most 
> circumstances.
> 
> Your description of how hard they are to remove suggests this may be 
> the case.  They work pretty darned good in steel but are not all that 
> easily removable from aluminum.
> 
> One quick way to tell is to see if they are hollow all the way 
> through.  If they are NOT, then they aren't what I'm talking 
> about.  If they are hollow all the way through, they just might be.
> 
> The advantage to the manufacturer is that they are just a quick as 
> pop-rivets to install.

Hmm... I'm not at home now so I can't check, but I think they are hollow 
all the way thru. 

The crazy thing is... they're threaded just like any other screw. I 
wouldn't expect you to be able to unscrew rivets.
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