The systems, stages, pipes and structures a job draws with.
Manage Utilities opens systems, stages, pipes and structures in one window - the schedule of what this job is built from, which you set up once and then draw with.
A pipe carries its size and its class, which the takeoff reports against.
A structure carries two independent things, and the difference matters:
Changing the symbol never moves an item between vendor buckets. Pick the category for where it should be bought, and the symbol for what it should look like.
The Code on a pipe or structure is the bid item code from the project's bid schedule - the pay item it bills against. It is not an abbreviation of the name. The readable identity belongs in Name; the seed catalogs ship with Code empty for exactly that reason.