These Dubro Swivel Ball Links work better than the traditional ball cups and ball studs.  The have less play, swivel with less resistance, and offer better height adjustments for eliminating bumpsteer. The plastic threaded hole area is designed for 4-40 turnbuckles  and the swivel ball is designed for 4-40 screws.  So this set of Dubros would be used for your steering arms (or center shock).  This second picture shows what we are referring to:

These are sold in pairs.