This is a slightly convex surface with the apex of the curve accurately centered on the fiber, so that when the connectors are mated the fiber cores come into direct contact with one another.[19][20] Some manufacturers have several grades of polish quality, for example a regular FC connector may be designated FC/PC (for physical contact), while FC/SPC and FC/UPC may denote super and ultra polish qualities, respectively. Higher grades of polish give less insertion loss and lower back reflection.