These two parts were designed to be mounted onto an aluminum extrusion to hold a filament spool. It is used in the Artifex 3D Printer (http://www.3dmakerworld.com/artifex), and can be used in MendelMax and other aluminum extrusion based printers as well. Installation instruction is provided in the Artifex Build Instruction: http://www.3dmakerworld.com/support/documents. The model was designed in Alibre (now Geomagic), and the source files can be found here: https://github.com/3dmakerworld/artifex.