The 15.01.603 bar clamping collet sleeve for the main spindle 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 convert the axial pullback of the 1501601 bar clamping draw tube into radial clamping force on the 9017E bar clamping collet through the coupling between the internal tapered seat of the sleeve and the working tapers of the collet. During closing, the draw tube pulls the collet axially into the sleeve; progressive contact on the tapered surfaces generates controlled compression of the collet around the bar, creating stable, concentric and repeatable holding. The clamping coupling acts on both tapers of the collet and the sleeve, distributing the load more evenly and helping maintain the correct bar position in the main spindle during rotation, feeding and machining. In the 25mm diameter variant, the sleeve has an even more important role because the bar has higher mass, inertia and operating loads than smaller diameter configurations; incorrect closing force may generate slipping, axial micro movements, vibration, loss of concentricity, cutting instability and reduced cycle repeatability. From a kinematic point of view, sleeve 1501603 works within the bar clamping chain of the main spindle: it receives the axial action of draw tube 1501601, guides and contains collet 9017E, converts axial pulling motion into radial closure, keeps the bar aligned with the spindle axis and works together with key 1501608 to ensure consistent integral rotation between collet, sleeve and spindle group. Correct sleeve operation therefore affects not only bar clamping but also motion continuity between the feeding system, main spindle, spindle drum and machine machining sequence. A stably clamped bar allows subsequent operations carried out by front tool spindles, radial slides, axial slides and auxiliary systems to work on a correctly positioned workpiece, reducing dimensional errors, form errors, geometry defects, concentricity variations and transfer problems between stations. The 15.01.603 sleeve must be carefully inspected during preventive and extraordinary maintenance, especially on the internal tapered seat, because wear on the inner taper diameter reduces the effective contact surface and causes a significant drop in collet clamping force. When the inner taper is abnormally polished, scored, ovalized, worn or no longer uniform, collet 9017E may close with reduced effectiveness on the bar, making adjustment of the closing force more difficult and increasing functional play. In these conditions, replacing the sleeve becomes necessary to restore correct force transmission between draw tube, sleeve, collet and bar, avoiding excessive compensation on the adjustment system that does not solve the mechanical cause of wear. For maintenance departments, machine tool builders, automatic turning shops, automotive production and precision engineering, this component is a critical spare part for maintaining clamping reliability, dimensional precision and production continuity on Gildemeister DMG Mori AS20 GS20 GM20AC multi-spindle lathes. Tadaah offers the 15.01.603 bar clamping collet sleeve as a technical component to be assessed not only for dimensional compatibility, but also for its kinematic function in the bar closing chain, main spindle stability and overall machining quality.