This is the OEM brake Master Cylinder found on Nissan 370Zs and Infiniti G37s with the Sport Model (Akebono) Brake Package.
The brake master cylinder is responsible for converting the mechanical force from your feet to hydraulic force to compress the brake calipers. When the brake pedal is depressed, brake fluid is forced through the brake lines and compresses the pistons and brake pads to stop the car. Over time, the seals in the brake master cylinder break down and can allow the fluid to pass the seals, resulting in a loss of brake pressure.
Not intended for use on NISMO models.
For drivers looking to increase driver feel and reduce firewall flex, Z1 offers a master cylinder brace that can be used with all OEM brake master cylinders found HERE.