The Wilhe's Raptor Adaptor is the first step by the e-NABLE Lab at the Rochester Institute of Technology in developing a modular system that connects a 3D-printed hand as an alternative terminal device to a prosthetic arm. This modular system will evolve into 3D-printed terminal devices that can be used by professional prosthetists and e-NABLE volunteers on various kinds of prosthetic arms. This will eventually allow the prosthetic hand technology developed by e-NABLE volunteers http://enablingthefuture.org/  to be used for prosthetic arms as well as for wrist-actuated prosthetic hands.  Meanwhile, power users of Tinkercad can build on the Tinkercad design https://tinkercad.com/things/8rOq92c76jG along with the STL files herein to customize their own variations of the free and open source design. The 3D-printed Raptor Hand can slide into the Wilhe's Raptor Adaptor without any modifications to the printed parts of the hand. Then the assembly is attached onto an unmodified existing prosthetic arm (with a pair of hooks and a harness) and the assembly is held together by zipties and screws. The STL files are sized for a 100% (small size for a 6-year-old child) Raptor Hand v2.2.  It is expected that future updates will provide more universal adaptors that will be easy to attach to a range of 3D-printed hands and prosthetic arms. http://youtu.be/91Pn5Bx2n6o Related prior art:The Raptor Hand by e-NABLE https://www.youmagine.com/designs/the-raptor-hand-by-e-nable#!design-documents  The Raptor Adaptor v1.0 https://www.youmagine.com/designs/the-raptor-adaptor-v1-0 Palm Cushion for Raptor Hand https://www.youmagine.com/designs/palm-cushion-for-raptor-hand   Adaptive Grip Mechanism https://www.youmagine.com/designs/adaptive-grip-mechanism-for-prosthetic-hand  The whippletree adaptive tensioner was derived from a concept by Steve Wood http://www.thingiverse.com/thing:392970