Coupling nuts follow the basic principles of all Nuts and Fasteners.

Thread Engagement is equal to or greater than the Bolt Diameter

With typical Finished and Heavy Hex Nuts assuring the threaded round bar is engaged to maximum strength is as simple as threading through the entire length of the nut. With Coupling Nuts the connection is often blind so it is important to gage the rod as the nut winds on. (Note: Coupling nuts can be manufactured with a site hole in the mid-point to assure full engagement.)