GT2 Arm Adapter

Scale by .3937 (1/2.54). This part is intended to hold a .25" by .5" arm. Has a 5mm pin and M3 setscrew hole. 80 teeth on the gear, based off an existing design that I can't seem to track down on Thingiverse, credit where credit is due. Inner diameter is 8mm, goes great with 608 bearings...