This is a Rear Wheel Cylinder for a Triumph TR7 with a 4-speed gearbox and Triumph TR8 all years. The TR7 4-spd and The TR8 5-spd and Automatic used the .75 bore wheel cylinder. The locating pin is on the left side if you are looking at the pin and bleeder as shown in the picture. The larger bore gave the TR8 more rear braking