Quark Masses

Mass of the Common Quark Finally Nailed Down in Science.
Currently there are six known flavors of quarks, each with a different mass. The masses haven't been known with much accuracy, in part because quarks are never found in isolation, they are are always found bound with other quarks. The binding interaction is so strong that most of the mass of the bound particle (like a proton or neutron) is due to the energy of interaction. These new theorectical calculations may give the quark masses to a greater degree of accuracy.