They have a long tube that is internally threaded and a plate with two clearance holes for rivets.
[2] The latter allows the nut to move slightly and so enlarges the positioning tolerances of the mounted parts.
They were originally developed for the aerospace industry but are now also common in automotive racing.
[3] Locknut types are available, which utilize deformed threads or a nylon locking element, much like a nyloc nut.
The nylon insert expands and stops vibrations of the nut and acts as a locking arrangement.