The 15.01.608 key for the main spindle bar clamping collet sleeve is a precision mechanical component designed for Gildemeister DMG Mori AS20 GS20 GM20AC multi-spindle lathes in the configuration for machining bars up to 25mm maximum diameter. Its main function is to ensure the kinematic connection between the 1501603 bar clamping collet sleeve and the 9017E bar clamping collet, preventing relative rotation between the two components and allowing integral rotation to be transmitted within the main spindle group. Through the mounting seat in the sleeve, the key works as a drive and angular reference element: it keeps the collet correctly oriented, prevents torsional slipping in the seat, stabilizes the coupling between collet and sleeve and allows the bar clamping system to rotate consistently with the spindle throughout the production cycle. In the bar closing group, the sleeve receives the axial action of the bar clamping draw tube and works with the tapers of collet 9017E to generate bar clamping; key 1501608 completes this function by turning the collet housing into a controlled kinematic connection capable of maintaining angular position and drive continuity during acceleration, rotation, bar feeding and machining. The role of the key is especially important in the 25mm diameter variant, where bar mass, rotational inertia and clamping loads are higher than in smaller diameter configurations; unstable drive could generate micro movements, vibration, localized wear, torsional play, loss of phase between collet and sleeve and reduced clamping repeatability. From a kinematic point of view, the key is part of the functional bar gripping chain of the main spindle: it connects the rotary motion of the spindle to the bar clamping collet, maintains bar orientation with respect to the rotation axis, supports clamping stability during axial pullback of the draw tube, contributes to cycle continuity with the spindle drum and keeps the system behavior consistent with operations performed by front tool spindles, radial slides, axial slides and auxiliary machine systems. Although it does not directly generate the closing force, it affects motion transmission quality and collet positioning accuracy, with indirect effects on functional concentricity, bar stability, dimensional control, surface quality, form errors and workpiece geometry. During preventive and extraordinary maintenance, key 1501608 should be inspected whenever sleeve 1501603 is checked or replaced, because compression marks, side wear, rounded edges, deformation, play in the seat or rubbing marks can reduce drive capability and compromise correct coupling with collet 9017E. For this reason, it is normally replaced together with the sleeve, avoiding the installation of an already worn element on a new or overhauled seat. Replacement restores the correct anti-rotation constraint, maintains integral collet rotation, reduces functional play and preserves the efficiency of the bar clamping group. For automatic turning shops, maintenance departments, machine tool builders, automotive production and precision engineering, the 15.01.608 key is an essential technical spare part for maintaining clamping reliability, cycle repeatability and production continuity on Gildemeister DMG Mori AS20 GS20 GM20AC multi-spindle lathes. Tadaah offers this component as a functional part of the bar clamping collet sleeve system, to be assessed not only as a simple coupling key but also as a rotational transmission, orientation control and kinematic stabilization element of the collet within the bar clamping chain.