This is a stabilization bracket for the Tevo Tarantula printer. In the stock printer the Z-Axis 'floats' on the flexible shaft coupling which creates some vibrations and compromises rigidity.
To install this you need 1) a standard 8x22x7 bearing and 2) some sort of 8mm shaft collar and 3) 2 x 4mm T-nuts and M4 bolts, which you should already have. The bearing and collar are available for cheap on Amazon. I made my shaft collar on my lathe but you can as well print your own using pretty much any material, see http://www.thingiverse.com/thing:400921
Sample Amazon listings:
I did print this bracket with 100% infill for maximum rigidity.
I recommend to place a 8mm washer (or something close to that) between bearing and collar so that the collar does not rub on the shielding of the bearing. In my case the shielding of the bearing was not flush with the inner race of the bearing but YMMV.