When marking an eye orientation, you have two options – vertical or horizontal. Both are acceptable, but require different different hardware. If you are ordering a Custom Sail and choose the “Adjust Sail to Fit Space” option, you will need to mark which you have, but shackles will be included.
Vertical Eyes mean the eye bolts or eye plates are perpendicular. These require Twist Shackles.
Horizontal Eyes mean the eye bolts or the eye plates are parallel with the ground. These usually require D shackles.
More Examples of Horizontal Eyes:
More Examples of Vertical Eyes: