It pays to check the loom before threading so any changes can be made ahead of time.
These are an example of typical wire heddles. Enlarge the photo to see the direction of the angle of the eye. These are installed for right handed threading. The eye slants from front to back, left to right. Because of the direction of the slant, it is more difficult to thread by someone who is left handed.
By flipping the heddle end to end, you can change the threading direction to left handed. The angle slants in the opposite direction (front to back, right to left).
It pays to watch which direction the eye is facing when putting heddles on the loom. When I was helping a friend thread a new-to-her loom, one shaft had the heddles backwards with a left handed angle, which made it awkward for threading and slowed the process. I have noticed it on a couple of my looms also. I think it is worth the time it takes to fix them and will do that the next time the looms are empty.
Many weavers are not aware of these differences and can't figure out why threading the loom doesn't go as smoothly as they would like. Take the time to fix the eye direction one time and have years of easy threading. It will be worth it!