None: This asset is not a spare part and is not linked to an inventory resource.
Spare part: The asset is linked to a non-serialized resource. Maintainable assets can be linked to tool resources. Components can be linked to material resources.
Serialized spare part: This asset is linked to a specific serialized inventory resource unit. Maintainable assets can be linked to serialized tool resources. Components can be linked to serialized (repairable spare) material resources. If you select this option, you must also select the specific unit to link to the asset. The status of the asset and the unit must match or you will not be able to link them.