Segmented helical dislocations, clearly distinguishable by Lang X‐ray topography (about 1 mm long and with pitches and diameters near 0.1 mm), are found in aluminum single crystals grown by secondary recrystallization under high vacuum (P≤10−8 torr). They are characterized by repetitive sequences of three distinct Bi segments which are not quite linear and are distributed in the order ... B1, B2, B3, B2, B1, ... .