Other than the boot, the original upper strut mount is the only factory piece reused on the new strut and spring. It's set in place, then the strut nut is replaced while the stem is held with a wrench. The Steeda spring is short enough that it's possible to compress it with your hands to get the nut started. From there, simply tighten the nut securely to complete the assembly of the new strut and spring. Also note that when putting the assembly back together, the large-diameter end of the spring must face down with the pigtail against the spring stops in the upper and lower strut mounts.