Looked at AMK catalog, did not find anything. They appear to have triangle threads, can't get a 5/16 course die on the screw. Similar type of triangle threaded design on convertible top fasteners. Google topic of triangle thread definition: Triangle self-tapping locking screws, Thread surface has a higher hardness. Therefore, when connecting, the screw can tap the inner hole of the bottom hole of the connector to form a connection. This type of screw features low torque and high locking.
Would like to find a source other than Used.
Thank you.