A beam compass, that is marginally better than some of the competing models. I personally like about it that it won't ever change it's value in the middle of the arc drawing, like usual compasses do.

Firstly, it may be used with almost any ballpoint pen, pencil or similar utencil

Secondly, it allows for precise positioning of the needle

Thirdly, it is nice to handle and can be firmly held in place while drawing.

1 M4 bolt is used for socket fixation and 1 2.5 mm nail is needed to make needle. A circle 8x12 rubber ring is used for smoothness of operation. 

1. Separate needle.stp into parts in slicer and place them on the print bed
2. Print out all the parts and assemble 
3. Assemble the beam onto the cylindrical beam part followed by the rubber ring, then glue on the cap
4. Gently tap the nail into the needle assembly until the point is approx. 3 mm proud
5. Cut the rest of the nail off the part
6. File off all the rough metal splinters and pointy tip