These parts are for the linear bearings. They will allow you to firmly tighten the nuts that will no more fell on the bed during a print. For more information, please visit : http://www.reppersdelight.spacymen.com/index.php/post/2011/01/22/Printing-Bogdan-s-bearing-blocks Look at the schematic render to see how many to print of each and where to mount them. They have been designed for easy mounting : the sliding rods can stay in place. They can all be printed raftless and without support. Part "BB_X_back_top" includes a physical support that can easily be broken afterward.