Cross Hire
Cross Hire (often referred to as Sub Hire) is used for tracking equipment that is on hired from a third party.
There is a few different methods to set up your Cross-Hire items, depending how accurate you wish your data on the Cross-Hire items to be.
But in all cases, you'll want to go into Setup > Item Related > Item Types and create a new non-hire Item Type called "Cross-Hire".
Often, Cross-Hire items come and go, as such General Placeholders & Per-Item/Supplier Placeholders tend to be more common.
But if you need to track each individual asset, you'd use the last option below "Specific Asset Numbers"