The Bosch PS31-2A is a 12-volt max cordless drill and driver with an adjustable clutch and a keyless chuck. The chuck holds any bit with up to a 3/8-inch shank, including drill bits and screw bits. When you turn the chuck sleeve clockwise, the three jaws move closer together, tightening around the bit. Turning the sleeve counterclockwise loosens the jaws. Should the chuck ever become damaged, remove it and replace it with a new one.
Flip the drill's direction indicator to reverse. Hold the chuck sleeve securely with one hand, and depress the trigger with the other hand to loosen the chuck. Remove the bit from the chuck.
Insert an Allen wrench between the opened jaws and into the screw in the back of the chuck. Rotate the screw clockwise to loosen and remove it.
Hold the chuck firmly in one hand once again, and depress the trigger to loosen the chuck from the threaded driveshaft. If the chuck spins in your hand and you cannot hold it securely enough to loosen it from the driveshaft, hold on to it with a pair of locking pliers.
Rotate the chuck counterclockwise until you remove it from the threaded driveshaft.