1 bag of bearings for MakerBeam contains 10 bearings, 10 M3 12mm squareheaded bolts with hex hole, 10 washers, 10 M3 nuts and 10 M3 self locking nuts. The bearing is 5mm thick. The outside dimension of the bearing is 13mm. The iinside diameter measures 3mm. If you fit it to a beam it will extend about 1,5mm from the edge of the beam. The 3mm inner diameter makes is easy to mount on a M3 bolt.