It is not a brush from what I can tell. However this can be solved simply.
First create a circle about the size you need it to be (this will be used as a guide).
Then create a vertical line (similar in length to the ones in the circle), and align the top point to the top edge of the circle.
Then with just your stroke selected use the rotate tool (R) and alt click the center of the circle.
This pulls up the rotate tool's dialogue box. Specify the angle (I used 2 degrees) and then click copy.
Once it has copied once, you can hold down Command + D (Control + D for PC) and repeat it until it makes a full circle.
Play with the angle degrees for larger or closer widths between lines.
This works with any path or shape.