Reflective marker with alignment feature

1. A device comprising a retro-reflective marker sphere comprising:

a core ball comprising:

a generally spherical body portion,

a mounting base extending from one end of the body portion of the core ball, and

a mounting recess having a recess opening in the mounting base and extending into the body portion of the core ball, and

a retro-reflective covering on the core ball, the retro-reflective covering comprising an opening through which the mounting base of the core ball extends,

wherein the core ball is a single-piece core ball,

wherein a flat lower surface of the mounting base is spaced proximally from a lower edge of the opening of the retro-reflective covering, and

wherein the mounting recess includes an interior screw thread for engaging an exterior screw thread of a mounting post when the retro-reflective marker sphere is mounted on the mounting post.

2. The device of claim 1 , wherein the mounting recess includes an upper portion and a lower portion, wherein the interior screw thread is part of the lower portion, and wherein the lower portion includes the recess opening and is larger in diameter than the upper portion.

3. The device of claim 1 , wherein the retro-reflective covering comprises only two pieces and wherein the opening in the retro-reflective covering is in only one of the two pieces.