The flyer holds the bar so that there is a space between their hands just big enough for both of their feet to fit side by side. (Saying 'two feet apart' would be confusing!)
The most common trick that uses this grip is the Whip.
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:
IMAGE CREDIT: Diana