Charlie Craven does a wonderful job in this video to help fly tiers understand how hooks are designed and for what purposes to use them. Charlie Craven’s video should really help beginner fly tiers.
In my opinion, there are no standards in hooks. For example, a size #12 dry fly hook from one brand may be longer or shorter than from another brand with no regard to the hook gap.
Charlie makes a good point near the end of his video, that not all brands are created equal in quality and cheap hooks are cheap for a reason.