The 14.01.251 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 20mm maximum diameter. Its main function is to convert the axial pullback of the 1501352 bar clamping draw tube into radial clamping force on the 9012E bar collet through the geometric coupling between the internal tapered seat of the sleeve and the working tapers of the collet. During the closing phase the draw tube pulls the collet axially into the sleeve; the 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 to maintain the correct bar position in the main spindle during rotation, feeding and machining. This sleeve is therefore essential for effective bar clamping, reducing slipping, vibration, axial micro movement and loss of concentricity, all of which can directly affect dimensional accuracy, surface quality, cycle repeatability and process stability. From a kinematic point of view, the component operates inside the bar clamping chain of the main spindle: it receives the axial action of the 1501352 draw tube, guides and contains the 9012E collet, converts axial pulling motion into radial closure, maintains bar alignment with the spindle axis and contributes to the functional continuity between the bar feeding system, the main spindle group, the rotation of the spindle drum and the machining sequence of the machine. Its efficiency is also important for the correct behavior of subsequent operations carried out by front tool spindles, radial and axial slides and auxiliary systems, because an incorrectly clamped bar may generate positioning errors, dimensional variations, cutting instability, form errors and transfer problems between the different stations. The 1401251 sleeve must be carefully inspected during preventive and extraordinary maintenance, especially on the internal tapered surface, because wear on the inner taper diameter change the effective contact area and causes a significant drop in collet clamping force. When the taper is worn, abnormally polished, scored, ovalized or no longer uniform, the collet may close with reduced force on the bar, causing loss of grip, adjustment difficulties, increased functional play and poorer clamping repeatability. In these conditions, replacing the sleeve becomes a necessary technical intervention to restore the correct transmission of force between draw tube, collet and bar, avoiding excessive adjustments that may only temporarily compensate for the problem without solving the mechanical cause of wear. For machine tool builders, maintenance departments, automatic turning shops, automotive production and precision engineering, this component is a critical spare part for maintaining cycle reliability, clamping precision and production continuity on Gildemeister DMG Mori AS20 GS20 GM20AC multi-spindle lathes. Tadaah offers the 14.01.251 bar clamping collet sleeve as a technical spare part to be assessed not only for dimensional compatibility, but also for its kinematic role in the bar closing chain, main spindle stability and overall machining quality.