This Borg & Beck clutch master cylinder, part number BCM123, is a high-quality replacement part designed for various Audi models including the A3, S3, and TT. With an inner diameter of 15.87 mm and featuring a sensor, this master cylinder ensures optimal clutch performance. It is compatible with several OEM references, including VAG 1K0721388A. Please use the vehicle's make and model tool to confirm compatibility with your specific vehicle. If unsure, contact us for assistance. This part is also known by cross-references from brands like ATE, BLUE PRINT, BREMBO, and VALEO.