Proflow Master Cylinder, Universal GM, Raised Top Aluminium, Black, 1.00 in. Bore, Dual Bowl, Ports Both side, Each - PFEMC1321BKPart Number: PFEMC1321BK Our Proflow aluminium GM style master cylinders bring a classy look to your GM or street rod. They feature all new components, raised or flat top style they will work on most GM vehicles equipped with power brake master cylinders. Polished or black finish. Manufactured from quality materials to ensure proper fitment. 1 '' Inch Bore Size High Quality Aluminum Chrome Finish 1 2 Inch 20 Thread 9 16 Inch 18 Thread