As you trace along the spine of a folding blade, away from the tip, there is a spot where it drops down at a 90 degree angle. This is the “run up.” It is the part of the blade which strikes the spring upon opening. Usually the run up shows above the edge of the knife as a sharp corner, which can tear one’s pocket, when the blade(s) is closed. If, when the blade is closed, there is no part of the run up showing above the handle the knife is said to have fully sunk joints. This is usually considered a sign of a better quality knife. If a very small amount of the run-up shows it is called a “partially” sunk joint.