This is spool holder that is small enough to print on a Printrbot Simple, which is what I used to make these parts.Requires two of these under the rim of the spool. You'll need a total of 4 608 bearings, 4 M8 25 bolts and nuts, and 8 M8 washers. Place one washer on each side of the 608 bearning and place into the slot. Run an M8 bolt through the slot and hold in place with an M8 nut. Do not over tighten as you can break the part.