A 3D printed extension for your thumb. Designed as part of an assignment for Intro to HCI.

The following video demonstrates a shake test and usability with a Fitt’s Law tester.


The thumb is the most frequently used when operating touch-screen mobile devices - yet also the shortest. Two features were core to my prototyping and design: a finger-like stylus tip and ring structure to secure the apparatus to the finger.


prototype 1

I initially wanted to include moving joints into my design, but I ran into difficulty making a robust design that did not hinder the natural movement of the thumb. So, I added rings and a fixed spine and kept the apparatus relatively short. This was in order to free movements of the thumb, such as extension and hinging.

prototype 2

Prototype 2 proved to be much more robust and easy to use - the spine bended slightly with each touch. However, it did not fit the finger well and restricted bloodflow. The stylus tip felt like a natural extension of the finger, but its touch surface area was too small. Thus, in later iterations the stylus is a modified paraboloid, angled off the spine and with the tip flattened.

prototype 3

Prototype 3 had better fit and was more secure. It was still a bit fragile, so in my final iteration I fattened the rings and added an additional ring for security.