Residual check valves hold a small amount of pressure in the brake system to keep the brake system functioning properly while helping to maintain a firm pedal. Maintaining system pressure prevents fluid from returning to the master cylinder when the master cylinder is positioned lower than or close to the same height as the calipers or wheel cylinders. Proper system pressure also keeps piston and wheel cylinder seals expanded, creating a positive seal and brake pads seated against the rotor. Valves include two 3/16" inverted flare fittings.