During the hot‑rolling of steel slabs, the large drive motor that turns the rolling mill’s rollers depends on a rotating‑contact assembly to transfer power from the stator to the shaft. The assembly key secures the brush‑holder segment of this contact assembly, preventing any axial movement that could cause brush misalignment or loss of contact during the intense start‑stop cycles of the mill. When the motor is engaged, the key locks the brushes in place, allowing the high‑torque output to be delivered smoothly to the rollers and keeping the process from stalling. In maintenance shutdowns, technicians remove and reinstall the key to verify brush wear and to re‑align the assembly, a step that restores reliable operation without the need for extensive disassembly. The same principle is applied in secondary steel‑processing lines, such as annealing furnaces, where the key ensures the drive motor’s contact assembly remains firmly seated, enabling continuous belt movement and consistent temperature control.