I wish I had a good close-up of the furrels, but mine look like the end of a Big diameter brake line with a flare in it so it has a collar to fit against the door trim bar. I would suggest steel, instead of the aluminium I have, as they tend to score slightly on the inside and then make it hard to get the pins in and out.
My pins are pieces of stainless steel rod, bent to the angle I wanted and then threaded on the end through the side window (see below) They work well (I stole the idea from Ola Miltrop on here - Thanks Ola!)
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