What are "loose pieces" and how do I promote them into a set?

Loose pieces are individual cars or engines in your collection that belong to a set but aren't linked to a tracked copy of it — usually because you logged them one at a time before adding the set.

Promoting them

Rather than re-adding the set and ending up with duplicates, you can promote your loose pieces: the app recognizes that you already own the members and wraps them into a tracked set copy, so they count toward completion instead of sitting on their own.

You'll see this offered around your sets and collection when loose members of a known set are detected.

Why bother?

Promoting gives you the completion tracking, set-level photos, and the ability to sell or list the whole set at once — all without creating duplicate records.

Related: How do I add the missing pieces to a set? and How does set completion work?