I've been guilty of calling mine both the K4BNT and the K5. I think one reason is the
wiki here on MR about Kindle Serial numbers. According to it, my device with serial number 9023 is a "Kindle 4 NoTouch Black (2012) / K4, K4B"
But yes, according to
Amazon, the black is the K5.
So...I just type whichever I feel like.