I found this on Thingiverse and now can't find the original. The bolt and nut print twice the size shown in the picture but I reduced it down by 50% on my Davinci 3D printer. This can be great for kids to play with or use it to build a screw in sensor mount if you hollow it out and place the sensor inside.
I used my Davinci 3D printer. I reduced the original size down by 50% within the Davinci XYZware. Then printed it in excellent mode (0.2 height, 30% fill). I discovered my Davinci had a cracked bearing when I printed the first one and the shape was oval not round. I did a youtube video showing how to replace the bearing mount. The final print was perfect.