What type of nut is this?

superscaniaV8:

Wheel Nut 3:
It’s called a DNF fastener.

Do Not Faff [emoji23]

[emoji38]so you think it may be a bugger to get undone?

Sent from my SM-N910F using Tapatalk

One of a range of “anti-tamper” fasteners, designed to stop us playing with things like microwave ovens. If they are reassembled wrongly there is a health risk from leaking microwave radiation.