Traditional Culture Encyclopedia - Traditional virtues - What are the circles on both sides of the slingshot?

What are the circles on both sides of the slingshot?

The picture above shows a traditional bow.

The picture above shows the Flying Tiger Bow.

The picture above shows no bow.

The picture above shows the catch bow.

There are also some personal bows, such as crooked handle, Iron Man's bow door series, stick bow, frameless and so on.