A little advice before we start!
Be careful!
I made barbed wire with 0,5 mm and it really has the potential to do some damage!! Even with 0,2 mm you should be carefull.
While the wire itself is very thin and breakable, short spikes won't bend and thus can cause some damage!
On the upside, people might avoid to touch your miniatures because of fear of tetanus.
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You will need:
- Fine Wire - I tried 0,5 mm and 0,2 mm. I think the later is better. You can get it from hobby stores. I recently bought ~ 1 km from ebay. You could strip small electric wires or network cables. There's usually some fine twisted wire inside.
- electric screwdriver / small drill
- pliers
- a piece of bigger wire, like a paperclip

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1st step:
- Take a piece of wire (I used a piece of about 30 to 40 cm) and fold it.
- Then take the paperclip or a piece of it and clamp it in the screwdriver / drill.
- thread the wire through the clip

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2nd step:
- hold the other end of the wires and twist them with the electric screwdriver / drill

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3rd step:
- clamp the clip to a vice or something else that will hold it

Here you can see how thin the wire is. It may break if you twist / bend it to much!