Draftex Ruling Pen is a traditionally designed instrument that lays down lines in ink, paint or any liquid medium that has the viscosity to flow.
They work in an incredibly simple way. There are two sides to the clip like ruling section that are held on a handle.
The tip of the two sides is adjustable via a small thumbscrew to varying widths.
Ink or your other chosen medium is dropped in the space between the two sides of the clip with an eyedropper or the whole tip of the pen is dipped in.
The liquid becomes suspended between the two sides down at the tip.
When you run the ruling pen along on your paper the capillary action transfers the liquid down to draw your line.
The width of that line can be adjusted as stated above by the thumbscrew.
It is a very simple concept that works well when understood. The versatility of being able to draw a line with anything that flows is a great attribute.
Care needs to be taken when handling as everything relies on the pen remaining upright during use.
When finished ruling you should empty any remaining ink as if laid down full any ink will leak out of the side.