Give a part its own list of approved replacements. A part substitute records that another part can be used instead of this one, and the rule applies everywhere the part appears — in every project, BOM entry, and purchase list. You keep the real part in your BOM, and PartsBox treats its substitutes as equally valid when it prices, purchases, or builds.
This is the level to use for passive components with many functional equivalents. Say you stock the Samsung CL05A104KA5NNNC and have approved the Murata GRM155R61E104KA87D and the TDK C1005X5R1E104K050BC as replacements. Add the two as substitutes of the Samsung part, and each of the three keeps its own separate stock, its own offers, and its own history. Nothing is merged — the substitute list only records what may stand in.
That is the difference from a meta-part. A meta-part is a new part with its own name that you put in the BOM, and it shows the combined stock of its members. A part substitute leaves the original part in the BOM and groups nothing. Use a meta-part when you think of the group as one line; use part substitutes when you keep the specific part but want fallbacks. For a substitution that should apply to one project and nowhere else, use a BOM substitute instead.
PartsBox suggests substitutes for you. Open a part and it lists likely equivalents, drawn from what other users treat as interchangeable, most common first. Review the specifications and add one with a click; PartsBox creates the linked part if you do not already have it.
Substitutes are carried through pricing, purchasing, and builds. Offers are gathered across the part and all its substitutes, and the best one wins, so a substitute can lower the price, not only cover a shortage. When a line comes up short during a build, stock of an approved substitute counts, which is how a shortage stops blocking production — the approval was recorded back when there was time to think about it, not during the scramble.
At pricing and build time PartsBox combines all three levels of substitution — the entry's own substitutes, the part's substitutes, and meta-part members — into one set of parts that may fill each line.
A substitute must share the part's unit category: a part measured by length can be replaced only by another measured by length, and a part counted in pieces only by another counted in pieces.
Part substitutes are in every plan, including the free Maker plan.