My lowers needed a spacer and they were supplied in the kit. As Mike said earlier, make sure the taper seats correctly -- that's what keeps the stud from working its way loose. A taper fit ensures that the stud does not wobble around from lateral loads where a straight shank would rely on clamping force alone which is not as reliable as a taper, especially where only one fastener is used. Ball joint studs experience more lateral loads than tensile loads so that's why the taper design is the standard. There is nothing fundamentally wrong with adding a spacer on a fastener, in fact engineers sometimes specify a spacer where it seems odd to have one. They may do this to gain stretch to mitigate high cycle fatigue failures or to ensure that the shank is in shear rather than the threads. A fastener (bolt) is like a spring. To maximize clamping force and help prevent it from loosening it gets tightened enough to stretch it to around 75% of its proof load. This is not necessary on a tapered shank ball joint stud. If the taper fits correctly there is no problem using a spacer or washer to align the castle nut with the cotter pin hole. And while I'm anal about torquing fasteners, tapered ball joint studs is my exception. I don't get worried bout torquing a ball joint stud -- hand tight to seat the taper and line up the cotter pin hole and I'm done.