Well, these sticks are made of two parts with a "gummi" element in between. The two portions of the sticks are joined together by means of a threaded rod. Now, because the "gummi" element allows the hitting portion of the stick to flex every single time it hits the drums, the thread will be loaded in bending and it will eventually fail. This is what happened to one stick, I then used the survived one to check the construction and come to the conclusion above. There is no way to fix the broken stick.
At this price point, the design of the stick is IMHO flawed and it will result in early failures for the sticks. The failure did not even happen after a long time (3 months of daily use) and it left me quite disappointed.