I have included two Arms. One uses the 4x12x5 bearing that Robo supplies and the other uses the commonly available 4x12x4 bearing. Either bearing will work equally well. The Arm requires one m4-.7x20, one m2.5x10 and two m3-.5x20 socket head screws. The Amazon kit has all required screws and the bearing has an Amazon link.
My Arm gradually twisted over time eventually the plastic cracked. It is worth inspecting your arm to verify that it is okay, because I began to have feed problems that took awhile to track down. This design will never allow the bearing to twist and it very strong.
I would recommend using the included Cura Profile as a starting point. It is important for the support settings and prints slowly for maximum layer adhesion and strength.
For $25 you obtain all of the parts to print a replacement.
Included is the Cura Profile. The support settings are important because it can be difficult to remove the supports from the bearing hole.