If you have two iLok protected products, such as MachFive and MX4, you can store both authorizations on one iLok.
You can transfer authorizations from one iLok to another if you register both iLoks at iLok.com. Note that iLok.com is not a MOTU website.
Transferring authorizations onto one iLok is not limited to two MOTU products. For example, you can transfer your MachFive authorization to an iLok for a third-party plug-in.
It is also OK to run both iLok keys on a USB hub if this is more convenient for you.