secures a magnet to a standard-sized bicycle wheel spoke for detecting speed with a hall effect sensor. the form can be easily modified to accept a range of magnet sizes, but is provided to accept a 3/16" x 1/8" disc magnet (locally available in the US at Harbor Freight tools). we welcome derivatives designed to accept magnetic media of different sizes, please post them here on thingiverse to share.design process: http://bit.ly/6mtnVE more info: http://velosynth.comprint with your makerbot using the gcode or roll your own from the stl. the included gcode is for a .2 infill and takes about 8.8 minutes to fabricatefinish by tearing away the raft. go ahead and drop in the magnet while the plastic is molten, it'll help to hold it in tight (although you may need to add some glue, better check and make sure once it cools down)drill out the holes for the tensioning bolt with a 3/32" bitinsert the M3 nuts into the holes on the bottom of the forminstall the spoke magnet to the wheelthread the tensioning bolt through both nuts and tighten to achieve a good fit