Square of Thales

A practical application of Thales Theorem: Any triangle inscribed in a circle and that has it's hypotenuse as the diameter of that circle is a right triangle. 

Because the ends of all three arms lie on a circle, they also form a right triangle.

This is a handy way to quickly determine if a corner is square. 

I got the idea from a youtube video by Steve Maskery

The 2 pieces are held together by a 5 mm machine screw. I used a M5 x 10 mm. A shorter Flathead M5 could also be used.