A12-3

7/16 x 24 tpi male fully threaded steel nut, SAE (double) flare, .550” long. Uses 7/16” wrench. American thread master cylinder brake line nut for use with 3/16” o.d. tubing with SAE (double) flare. As the name implies, this is found most often at the master cylinder, but the A12-3 is also found on the back axle of some full size Ford trucks and other places. Most popular size of master cylinder nut.