Asteroid
The dwarf planet Ceres is by far the largest asteroid, with a diameter of . The next largest are 4 Vesta and 2 Pallas, both with diameters of just over . Vesta is the only main-belt asteroid that can, on occasion, be visible to the naked eye. On some rare occasions, a near-Earth asteroid may briefly become visible without technical aid; see 99942 Apophis.
M-type asteroid
16 Psyche is the largest M-type asteroid, and does appear to be metallic. 21 Lutetia, an anomalous, probably non-metallic body, was the first M-type asteroid to be imaged by a spacecraft when the Rosetta space probe visited it on July 10, 2010. Another M-type asteroid, 216 Kleopatra, was imaged by radar by the Arecibo Observatory in Puerto Rico, and has a dog bone-like shape.