The flyer places both hands, almost touching, in the middle of the bar. One hand is normal, the other is reversed. To turn to the left, the flyer reverses their right hand (first photo). To turn to the right, the flyer reverses their left hand (second photo).
This is the most common way to hold the bar for a half turn. Examples of tricks that use this grip are: Half Turn, Cutaway. Some flyers prefer to use a 'Close Turnaround Grip' when turning around.
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