This one is for hold the m8 rod on both side so that the printer will not vibrate and move. I screw it into the plywood base. My prusa i3 is from this store on aliexpress http://goo.gl/45e9sw but i dont recommended 3d printer from this store, if you want to buy one better go with this one http://goo.gl/GW6NhQ cause you can update the firmware for their printer. The store that i buy my printer is stuck with their melzi that we can't even upload updated firmware. If anyone have same printer please share with me what your upgrade for this printer :)