You can create an external business object. An external business object is not owned by you. It is an asset owned by a customer, that you add as business object for maintenance purposes.
You can use external business objects only on work orders and not on rental orders or rental quotations.

Standard procedure

1.	Go to Business objects > Business objects > All business objects.
2.	Click New.
3.	In the Serial number field, type a value.
4.	In the Item number field, enter or select a value.
5.	In the Organization field, enter or select a value.
6.	In the External object number field, type a value.
7.	In the Manufacturing date field, enter a date.
8.	Click Create.