It varies. I don't have my sails so I can't measure it for you, but North put them pretty close - maybe 24". Z-Sails is making a sail and said they would but them wider, I think around 30". Wider spacing means easier flaking, fewer folds, less wrinkles (I alternate the folds as it comes down). You should have one at the full-length batten (North did this with a grommet above and below the batten, and "Y" shaped webbing to the slug). Make sure you don't have one in the slot opening when hoisted, cunningham on, etc.
