I envision a Contact (ToLoanTo) database or table
Another table or db Equipment (EquipToLoan)
Another table or db OnLoan
Contact would have a unique ContactID field (automatic serial number when created)
Equipment would have a unique EquipID field (automatic serial number when created)
OnLoan would have at least two - ContactID field and EqupID field that would be filled in and link Contact and Equipment to the OnLoan database record.
You might also want to search this forum using the key words "Inventory Log". We've had several discussions here on a method where you'd log items in and out of inventory using a "check register" like layout where items are added and removed much like you would log "deposits" and "withdrawels".