This design is part of the ongoing work of the E-Nable group. 
For more information on where to connect with people who can help someone in need with sizing, printing and/or assembly a mechanical hand please join the e-NABLE Google+ Community entitled, e-NABLE: 
https://plus.google.com/communities/102497715636887179986 
For more information and stories: 
http://enablingthefuture.org 
https://www.facebook.com/enableorganization 
This is the third in a series of 3 things that, when combined, can be used as a device for some partial finger amputees missing more than half of their finger. It's customizable so that it can be adjusted to the size of the user's hand and fingers. 
Included in the "files" section is a PDF document with a measurement guide and instructions on assembly. 
* All measurements must be in millimeters. 
This thing contains the cable anchor worn on the back of the user's wrist as well as the snap-pin for the axle on the artificial finger. These files are static (non-customizable). 
A video showing someone trying out the device can be seen here:http://youtu.be/WlfS02OAKcU 
I see this as just a starting-point (and a rather rough one at that). I would love for other designers to take the source files, experiment, re-mix and improve upon this. :)