The flyer holds the bar with one hand, usually in the middle of the bar. Could be the left or the right hand.
This very rare grip is only really used on Novelty tricks like 'One-Handed Flying', but is included here for completeness.
Note that the image shows the flyer with their thumbs under the bar (around). This is the most common way, however some schools prefer the thumbs to be over the bar.
You can find out more about this trick in my books: