Pinhole Solar Eclipse Viewer
Small one-piece pinhole solar eclipse viewer.
SCAD and STL files included.
UPDATE: new version at https://www.thingiverse.com/thing:2469544 is longer to give larger image of sun, assembled from 2 identical printed pieces.
To use viewer: Point viewer with cross end toward sun and line up the bright dot (image of the sun) on the flat surface at the other end. During the partial phase of a solar eclipse, the dot will be party obscured by the moon, creating a crescent shape instead of a round dot. If you are fortunate enough to be viewing the eclipse within the path of totality, when the eclipse is total, you should even see a faint image of the sun's corona.
JPG image files show viewer in use with late afternoon full sun (several weeks before 2017 eclipse -- I couldn't exactly wait until the eclipse to publish the Thing, now could I?).