Hi Mate
Those are very diferent to the ones I have seen but I can see your problem or at least I think I can
I take it that the bit you have taken a pic of is a cross head on the end of an internally threaded tube
If the other end is a hex head I would suggest you find someone with a decent metal vice and grip the bit you have pictured in it (just the tip of the screw head) and then undo the other side
If no vice is available get a decent set of Mole Grips (locking pliers) and use them instead
As a permanent fix file a couple of flats on the side of it so you can use a spanner on it next time
Replace the internal bolt/screw each time you change it so as to keep a good head on it (machine screws/bolts are cheep if you buy bulk)
If I am wrong about the other side post some more pics
Jason