I was having great trouble identifying the plugs on my trailing socket, so l purchased this pen and wrote on each plug, the tip is maybe a little too thick but it works very well and does the job and does not rub off.
I've had two of these pens. The tip fell out the first one and the second one the ink kept flooding. If you want to draw a neat line don't buy this pen. The ink is watery and floods out the tip.. then when you try and use it again it has dried up. The worst pen I have come across in 60 years.