The default setup is for 3/8 inch carbon fiber or aluminum rods, which can be substituted for 3/8 Crossbow bolts, 3/8 inch chrome steel balls, and 3/8 inch N52 Neodymium magnets. The chrome steel balls are meant to be JB welded or TIG/MIG welded to the heads of 6mm M3 capshead bolts. Be careful if you MIG or TIG weld them, you can easily melt the M3 bolt from the heat, all that is needed is a few tacks.
For the Rostock or Rostock mini, print 2 of the boom ends, an effector, and 3 of my magnetic carriages, as well as 12 rod adapters if you have .199" OD Carbon fiber tubes for your arms (I would recommend ABS). Assemble everything according to the instructions in the SeeMeCNC forum thread, and make sure you use the jig mentioned in the description to get consistent length arms, or they can become disconnected mid print
For the Rostock MAX print all of the same things, except for my carriages and the rod adapters, unless you want to use .199" CF arms on your MAX. Instead of the carriages, print the Cheapskate 90 degree ballends. The assembly is pretty much the same.
It is a good idea to read some of the forum thread to get an Idea of what to do an not to do while assembling, though before screwing the balls onto anything, you should tap the hole with either an M3 tap or by forcing an M3 bolt into it. Make sure not to strip the threads you create in the plastic, this is what keeps the ballbolts secured. Also, try to avoid putting torsion strain on the JB weld, It probably will break, AKA, dont twist the balls on by hand, especially if they are resisting threading into the hole. use a small pair of needle nose pliers instead.