Abstract: In the compression molding of a fixed angle centrifuge rotor utilizing discontinuous fibers, sample tube apertures cores present in the net-shape mold are covered with pre-cured sample tube aperture inserts. The sample tube aperture inserts have a constant and unchanging inside diameter and are formed from composite fiber. This composite fiber extends from the closed bottom of the inserts, upwardly along the sides of the inserts to the open top of the inserts to provide tensile strength longitudinally of the sample tube aperture inserts. The sample tube aperture inserts have a regular and smooth inside for first accommodating the sample tube aperture cores when the rotor is compression molded and later the sample tubes themselves when the rotor is fully fabricated. These inserts have an irregular outside for forming an interference fit with the subsequently formed compression molded rotor body.