30 The genitive noun πυρός (puros) has been translated as an attributive genitive (see also Rev 1:14).
31 For the translation of διάδημα (diadēma) as “diadem crown” see L&N 6.196. Diadem crowns were a type of crown used as a symbol of the highest ruling authority in a given area, and thus often associated with kingship.
32 Grk “head, having.” Because of the length and complexity of the Greek sentence, a new sentence was started here in the translation.
33 Although many translations supply a prepositional phrase to specify what the name was written on (“upon Him,” ; “on him,” ), there is no location for the name specified in the Greek text.

In other versions

His eyes are like a flame of fire, and on his head are many diadems, and he has a name written that no one knows but himself.

His eyes are like blazing fire, and on his head are many crowns. He has a name written on him that no one knows but he himself.

His eyes were like a fiery flame, and many crowns were on his head. He had a name written that no one knows except himself.

His eyes were like flames of fire, and on his head were many crowns. A name was written on him that no one understood except himself.

Now his eyes were a flame of fire, and on his head were many royal headbands having a name written that no one except he himself knows.

His eyes were as a flame of fire, and on his head were many crowns; and he had a name written, that no man knew, but he himself.

Public Domain