- https://en.wikipedia.org/wiki/Threaded_fastener - a discrete piece of hardware that has internal or external screw threads. It falls into the overall fastener family. They are usually used for the assembly of multiple parts and facilitate disassembly.The most common types are the screw, nut and bolt. Other more specialized types of threaded fasteners include captive threaded fasteners, stud, threaded inserts, and threaded rods.
- https://en.wikipedia.org/wiki/ISO_metric_screw_thread - the worldwide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in 1947.The "M" designation for metric screws indicates the nominal outer diameter of the screw, in millimeters (e.g., an M6 screw has a nominal outer diameter of 6 millimeters).