I have a Custom Item Model on my Head, but I want Different Model in my Hand (1.21.5)

This is the command that I use to get a helmet with a custom model on my head rendered when equipped. 
/give @p minecraft:iron_helmet[item_model="diaz:h1m",equippable={slot:"head"}]
This 3d helmet renders perfectly on my head, however I want a different Item model for when its in my inventory and hand (diaz:h1), what would the command be?