If I remember correctly the included cup is dropped over the strut cartridge once installed (increases the OD of the strut) then the gland nut is installed. The cartridge sat a bit low in mine and I had to add a 1-2 fender (large diameter) washers to shim it up where the gland nut would contact and secure the top.
See link for Strut, Cup, Gland nut, Shock top nut pic.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1