Custom Parts are items in Spectrobes and Spectrobes: Beyond the Portals that can be equipped onto Adult or Evolved form Spectrobes. Each part changes the same part of the Spectrobe, and only one can be equipped at a time. There are two types of parts: attack and defense. While they raise either the attack or defense of a Spectrobe, they also decrease the other (not the case in the original Sprectrobes however?).
In the original Spectrobes, Custom Parts are obtained by digging up a fossil with no or very little damage, and can only be equipped after analysing the Epsilon cube, which can be found far from the landing point in Genshi, area 1.
In Spectrobes: Beyond the Portals, Custom Parts are obtained by excavating Mystery Stones, which can contain Custom Parts for the Spectrobes that can be excavated on that planet. They can be found on every planet except for Darkmos and Malik, since Dark Spectrobes cannot be equipped with Custom Parts.
Custom Parts also appear in the Spectrobes webisodes, where they are called Customized Parts by Jeena at the end of episode 14. The Custom Parts are first found by Professor Wright in episode 12, where they are unearthed on Genshi. Jeena starts to customize them in episode 13, and she gives them to Rallen's Leozar and Rydrake in episode 14, which increases their power enough to where they can defeat Maja's Pinorska.