Interior threads are noticed on the inside of nuts, where by a bolt (with an external thread) is screw into. When discussing screws we have been referring to Exterior Thread. Broadly Talking here are two different types of Thread: The look to the travel during the head of your screw https://types-of-perimeter-barrie49260.ampblogs.com/considerations-to-know-about-different-types-of-screw-heads-66178668