This is a finely made antique brass disk bob pendulum. It is stamped on one side with the name PATEY in tiny letters. It is 9 inches long, which means it is a half second wall or mantle clock pendulum with a one second period. The period of a pendulum is defined by the distance between the hook pivot and the center of mass of the pendulum bob. The screw wheel on the base of the bob allows the pendulum period to be adjusted small fractions of a second. The bob is aerodynamically shaped to reduction air friction.
The name Patey on the pendulum may refer to the British clock retailer, William Patey of Manor Gardens Holloway London. If so, this might date the pendulum to early in the 19th century.