Zinc diecast round eye swivel thumbnail snap hook is a type of hardware commonly used in various applications, such as in the manufacturing of bags, backpacks, lanyards, keychains, pet leashes, and other products that require a secure and easily detachable connection point. 

Zinc diecast: This refers to the material used in the manufacturing of the snap hook. Zinc diecasting is a process where molten zinc is injected into a mold to create the desired shape. Zinc is a popular choice for snap hooks due to its corrosion resistance and strength.

Round eye: The "round eye" part of the snap hook refers to the shape of the attachment point. It's a circular loop or eyelet through which a strap, rope, or other connectors can be threaded or attached.

Swivel: The term "swivel" indicates that the snap hook can rotate or pivot at the connection point. This feature allows for more flexibility and prevents tangling or twisting of the attached items.

Thumbnail: "Thumbnail" in this context refers to the shape of the lever or trigger used to open and close the snap hook. It's called "thumbnail" because it is typically designed to be operated easily with the use of a thumb.