Hope things done on a ShapeOko 3 are okay:
Source file: http://www.shapeoko.com/wiki/index.php/File:Tool_calipers_locking.svg
CAM done using MakerCAM and F-Engrave.
Parts list: 6061-T6 aluminum, brass Chicago screw, #8-32 screw, #6-32 screw (may need a divot filed into it), and a knurled #6-32 thumb screw
Cut on a ShapeOko 3 using a Makita RT-0701 and 1/8" bits, feed 215mm/min., plunge rate 27mm/min., 0.2mm cutting depth.