12mm linear Bearing

These linear bearings need to be press-fit into the object you would like to slide on your rail or shaft. The outside diameter is 21mm so the hole you drill should be no bigger than that. The press-fit can't be too tight though or the bearing will not slide properly on the shaft, if the bearing won't go in via an arbor press then you will need to drill out the hole slightly larger. If the fit is a bit loose then you can just use some red Loctite to lock things in place.