Abstract: A weft thread pre-winder or pre-spooling device for an air jet loom includes a thread storage drum (6) made up of several drum segments (7) that are each adjustable in the radial direction so as to adjust the diameter and circumference of the thread storage drum. Thereby the amount of stored thread can be adjusted. Open gaps or interspaces (8) are formed between respective adjacent drum segments (7), and become larger or smaller depending on the radial adjustment of the segments. Especially for threads that form only a small thread balloon while being drawn-off from the thread storage drum, the threads would tend to get into these interspaces and become caught on the edges or corners of the drum segments, which would lead to energy losses in the thread and interfere with the proper weft insertion and thread transport.