These proportioning valves are similar to what GM used on many cars in the 70s. They are non-adjustable and may require an adjustable valve in the rear brakes (if needed). Block incorporates metering (for front brakes) and proportioning (for rear brakes) into one unit. For use with front disc, rear drum brake systems. Includes hard lines to connect to a master cylinder with 3/8"-24 outlets. Item Details For M/C with 3/8"-24 outlets.Bottom Front Port: 3/8 "-24 IFF threads - goes to one front brake Top Front Port: 3/8 "-24 IFF threads - goes to one front brake Middle Top Port: 1/2 "-20 IFF threads - comes from master cylinder Rear Top Port: 7/16 "-24 IFF threads - comes from the master cylinder Rear Most Port: 9/16 "-18 IFF threads - goes to rear brakesBottom Front Port: 3/8 "-24 IFF threads - goes to one front brake Top Front Port: 3/8 "-24 IFF threads - goes to one front brake Middle Top Port: 1/2 "-20 IFF threads - comes from master cylinder Rear Top Port: 7/16 "-24 IFF threads - comes from the master cylinder Rear Most Port: 9/16 "-18 IFF threads - goes to rear brakes