The line is: His grip was ironplz help
Was the sentence 'His grip was like iron' or 'His grip was iron'? It makes a difference. The first one is a simile because it contains the word 'like'. A simile it a way of comparing aspects of two things. The second one is a metaphor. It is saying that his grip IS iron. Which it isn't. Writers usually do this to show that they share the same characteristics. That is, iron is strong and quite difficult to break, so saying 'his grip was iron' is roughly equivalent to saying 'his grip was strong and quite difficult to break'.
