Of the three most common chokes, "full" is the tightest. It keeps the pellets together over a greater distance and is therefore used for longer shots, generally between 40 and 45 yards.
This choke is not as tight as the full choke and is used for mid-range shots, usually between 30 and 40 yards.
Improved Cylinder Choke
This choke barely controls the spread of the shot and is used for shots between 20 to 30 yards.