What are bolt circles and how to create one?

Firstly, you will need the paid Drawing or Bundle add-on for DesignSpark Mechanical.

Wiktionary defines a bolt circle as a theoretical circle on which the centerpoints of bolt holes lie when the bolt holes are positioned as equally spaced in a circle.

In DSM, a bolt circle annotation can only be placed in 3D mode on holes drilled in to solids. They are meant to show the diameter & angular separation of holes rather than just circles as a 2D surface pattern. It can be an application specific annotation: bolt circle for the lugs on a car's wheel, or the bolts on a bolted joint between pipe flanges (https://en.wiktionary.org/wiki/bolt_circle)

Watch this for a how-to: