Pressure residual valves are designed to maintain a small amount of line pressure needed in certain situations. The 2lb valve would be used with disc brakes whenever the master cylinder is mounted below or level with the calipers to prevent possible fluid drain back which can result in excessive pedal travel (4 wheel disc brake vehicle would use 2 valves, one in the front and on in the rear circuit). A 10lb valve would be used in any drum brake circuit no matter of the master cylinder location. Pressure residual valves are machined out of billet aluminum, are available with 3/8-24 inverted flare female or -3AN male threads and have a Black anodized finished.. Billet aluminum frame mounts are available separately.