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The B3103-771-0A0 Thread Tension Assembly is a high-precision spare part specifically designed for buttonhole (KAJ) industrial sewing machines, including models like the Juki LBH series. Built for durability and accuracy, this unit plays a critical role in controlling upper thread tension, ensuring consistent stitch formation even during high-speed operations. Crafted from premium materials and engineered to Juki's original specifications, this thread tensioner offers smooth adjustment and reliable thread control across various fabric types. It helps eliminate common sewing issues like loose stitches, thread breakage, or uneven buttonholes—making it essential for professionals demanding precise tension control in garment manufacturing. Whether used as a replacement or during machine servicing, this OEM-compatible part helps restore the original performance of your buttonhole machine, extending its life and supporting flawless sewing output.