1. Select a set of 3+ vertices, a chain of 3+ connected edges, a single polygon (3+ sides), or a multi-polygon selection.
2. Start the tool. A small modeless dialog opens with an optional radius override and an Apply/Circularize button.
3. Click Circularize (or set a radius first, then click Circularize) to reposition the selection’s boundary vertices evenly around their average center onto a circle.

The circle is computed around the selection’s average center; each vertex slides along its own centroid-to-vertex direction, so the selection’s existing shape and topology are preserved. Enable “Flatten to average plane” to first project the vertices onto the selection’s best-fit plane for a co-planar circle. Vertex placement respects the object’s active vertex edit constraint (None, Edge, Face, or Normal). Only works with Editable Poly objects and objects with an Edit Poly modifier.