Abstract: A top cap assembly for a shock absorber includes a cap which has a first locking member connected to the center thereof, and an inner plate which has a second locking member connected to the center thereof. A first section of a piston rod extends through the first passage of the first locking member and is restricted by the first ridge of the first passage. A second section of the piston rod extends through the second passage of the second locking member and is restricted by the second ridge of the second passage. When installing the top cap assembly to different shock absorbers with different diameters, only the first locking member and the second locking member need to be replaced, and the cap and the inner plate do not need to be replaced.