This is a replacement top cup that is 3D printed But An Upgrade From the Original! It is the exact same size as the originals (see photos) but it is made of a slightly flexible material! 
The flexible rubber material has nothing inside the barrel so it will just push it on and it will hold firmly without having to align it with the stem!
It works great and I hope you'll try it if you need one. 
Thank you! You won't be sorry!