Use Engineering Part Revision/Spare Parts to register spare part lists; you can also use the right mouse button menu option Add To Spare List in Engineering Part Revision/Multilevel to add a part in the structure as a spare part. Any defined part can be used in a spare part list, and any item can have a spare part list. The spare part list is meant to be a list of the material/parts you expect to need when performing maintenance to the part. This will be the engineer’s best guess on which parts should be kept as spares for the item.
The spare part list can later be copied to a project item in Project Delivery and, still later, be copied with the project item to Maintenance. Spare parts are used in maintenance when active parts fail. Having spare parts can give you shorter down period when an active part has a failure.