WaycreatStainless Steel 1 Inch S Hooks Connectors S-shaped Hook, 80-pack JJIUS019135

Q: What is the diameter of the hook?

The widest part of the hook is exactly 3/8" wide outside-to-outside. Then narrowest part is 1/4" inside. So you can just barely fit the hook through a 3/8" diameter circle and you can just barely fit the hook over a 1/4" diameter rod. The longest dimension of the hook is just a small fraction of an inch over 1", essentially 1".