This accessory is used together with my X-axis tensioner (see:http://www.thingiverse.com/thing:253357) to be able to adjust the belt correctly if you want to change the belt type. In my case i´m using a GT2 belt with 2 pulleys á 16 teeth. Because of changing the original pulley diameter to a smaller one, i searched for a better way to adjust my new belt system. Update in progress: You need: 4x M3x16 bolts for the motor mount 4x M3 washers 2x M3x20 bolts with nuts for mounting the switch the 2 M5 bolts of the original motor mount and the nuts already placed in the frame.