This banjo bolt is a direct, bolt-in replacement for the factory pulsation damper located on the primary fuel rail on 1984 through 1988 RX-7s.
The pulsation damper eventually wears out and causes a dangerous fuel leak directly on top of the engine, which can then leak down onto the hot exhaust manifold causing a catastrophic engine fire. 1989 and up models featured a redesigned fuel rail and damper, though leaks have still been reported by owners.
Simply remove the pulsation damper from the primary fuel rail (requires removal of upper intake manifold, see the Fuel/Emissions Control section of the Factory Service Manual here), then screw the banjo bolt in its place. Proper torque is 15-20 ft/lbs. Do not overtighten and do not re-use crush washers.
After installation, be sure to check for fuel leaks before running the engine by jumpering the two terminals together on the yellow Fuel Pump Check Connector located near the passenger’s strut tower and turning the key to ON. This will allow the fuel pump to run and pressurize the rails for inspection.