For my FUE procedures I like the hair to be a number 0 clip on the clippers. Sometimes I go a little bit shorter. It also depends on how straight the patients donor hair is. But usually the length is 1-2mm.
Usually FUE hairs are about 1mm to 2mm. Sometimes longer depending on the preference of the surgeon. In general FUE extraction of eyebrow hair is NOT recommended because FUE extraction will leave a scar.
I stress this again: FUE extraction of your eyebrow hair WILL LEAVE A SCAR.
We generally do this with either a strip surgery with long hair, or a long haired FUE. To do this right, you have to align the hair angle in the proper direction so that the hair grows flush against the skin. A very short hair from an FUE with a 1 mm shaved hair graft, would not show the hair direction. That means that the ideal direction would not be certain., so I prefer a very small strip surgery. See the web reference below for a more extensive discussion which I wrote for one of my other websites.
How Short before FUE Harvesting
Hair transplant surgeon needs to be able to see the angle and curvature of your hair in order to properly aim and harvest them. I usually trim it to 1mm length but I can go as long as 3mm too if I have to.
Removing hair transplants
Hair transplants can be removed with electrolysis. Laser hair removal works for large areas and is not as precise as electrolysis and not suitable for eyebrow hair transplant removal.