a method of assembling a spring inside of a tube includes providing a coil spring and a tube having a first retaining structure at a first end of the tube . the method includes positioning a rod in the tube . the spring is positioned in the tube , and a second retaining structure is attached to the rod with the spring positioned between the first and second retaining structures . a force is applied to the spring , and the second retaining structure is fixed at a position wherein the spring provides a desired preload .