Illustrator 1px round brush?

I was wondering if there was a 1 pixel round brush on Illustrator, if not how could I achieve that with this for like a stroke that is curved? Like this: http://puu.sh/5B56F.png

Because it's obvious you can just slap a circle at the end of it because it's at a radius and making a circle fit that end would be very much a headache.

I've also tried using the 5 point brush and shrinking the size down to 0.1px but it looks a little off, especially when you actually compare it to a actual circle.