I don't see a need for the join table if an item can only be a member of one set.
Set::__pkSetID = Items::_fkSetID
PhilMod - your suggestion works well - no join table needed. An ancillary question though - I noticed in the latest version of FM Pro there is a summary field calculation for "List of". I am thus in the Set table trying to get a summary calculation for a list of the ItemIDs in a Set. However, only the current active ItemID shows up. For example, if my active Set has links to two Items where Item IDs are #1 and #2, I want to see my summary field showing both #1 and #2. I have tried to show the summary calculation both summarizing repetitions as "all together" or "individually" but get the same single result. Am I going about this the wrong way? How can I get a summary of the ItemIDs that are all linked to an individual Set in one field on the SET table?