A men’s automatic watch is also referred to as a self-winding watch, this type of watch is a mechanical watch because it mainspring inside of the watch is wound automatically through the natural motions that the wearer happens to make by moving his wrist while wearing the watch. This lets the energy from that motion run the watch, so it isn’t necessary to wind the watch by hand. Today, most mechanical watches that are sold are self winding.
Men’s automatic watch movements are almost the same as a manual movement with the addition of a certain mechanism. This mechanism is powered by a weight that winds the mainspring. Inside of the watch is what people call a rotor this is an eccentric weight that turns on a pivot within the case of the watch. The normal movements of a person’s arms and wrists are what cause the rotor to move back and forth on its staff, the staff is connected to a ratcheted winding mechanism. The motion of the wearer’s arm is then changed into the circular motion of the rotor, and through many different sized gears the rotor eventually will wind the mainspring, as well.
With modern self-winding mechanisms there are 2 ratchets and they wind the mainspring in both clockwise and counterclockwise motions. A mainspring that is fully wound can last around 2 days on the stored energy reserve; this allows them to keep running at night while the men’s automatic watch isn’t on the wrist. Many times these men’s automatic watches can be wound manually by turning the crown, this way if the watch is not being worn it will still run. A major problem had occurred in the past with wrist watches that continue to wind when they are already full, causing the mainspring to break or make noises. So a slipping clutch was devised to be put inside the mainspring so it cannot be over wound.