Abstract: The present invention is a clock head assembly that writes reference marks on a magnetic disk of a hard drive. The clock head assembly includes a clock head that is mounted to an arm and coupled to the magnetic disk through a window of the disk drive housing. The arm is pivotally mounted to a housing which has a gasket that seals the window and allows the assembly to operate in a non-clean room environment. The arm is coupled to a cam that is manually actuated by a lever to move the clock head arm assembly between a loaded position and an unloaded position. An alignment plate is also provided for aligning the clock head assembly to the hard drive assembly.