How to make WWI German patter caltrops

Specifically how to make WWI German pattern caltrops.

I ran across this online in museum collection sometime ago and made a few and kept the pattern just in case. I had some time spare earlier in the workshop and thought I'd make some more as they are relatively simple to make.

I must admit to not knowing a lot about the WWI German industrial machine, but have been told that caltrops like this may have been made by blacksmiths for the war effort and packed into shells to be shot at supply/transport links to injure horses and the early rubber tyres. Can't vouch for any of it except the museum piece.

The caltrop seems as old as warfare, being used as an area denial weapon for centuries.

In fact I just did a quick search on WWI caltrop and came up with something very similar: http://rustywarrelics.co.uk/products/...

The oil quench at the end is for me as it means they will survive until the market I trade at, the International Living History Festival in April 2017. http://www.livinghistoryfairs.co.uk/