MAC address too long for Network Address value field

I'm trying to go into the properties/configuration for my network adapters and manually set the Network Address value to one of the random MAC Addresses from your generator. But the generator is generating MAC addresses that are too long. The Network Adapter field cuts off after 4 pairs of characters (i.e. 67:8c:c6:59) , but the random MAC Address Generator is giving codes that are 6 pairs long (i.e. c6:3e:f3:fa:b0:77).

What's the difference between the longer MAC addresses that are being automatically generated and the shorter ones that my Network Adapter's value field is maxed out at? How do I generate one of these shorter Network Adapter MAC addresses?

Thank you in advance.