During my work at Tikkun Olam Makers (TOM), we developed a simple 3D printed prosthetic arm with interchanging add-ons for different uses. The project is fully open-source, and all CAD files and assembly instructions were immediately uploaded to our website. The interest and demand led us to develop the Parametric Prosthetic app, which gives a wide solution for size customization. With a click of a button, users can get custom sized prosthetic arm that they can print and assemble easily, anywhere in the world.