314.23(H)(1): A box shall be supported from a multiconductor cord or cable in an approved manner that protects the conductors against strain, such as a strain-relief connector threaded into a box with a hub.
As I read this, it doesnt'
require a box with a hub; that is simply a suggested method to achieve the required strain relief. As far as I can tell, a Kellems grip achieves equivalent strain relief when used with a four-square box, and thus meets the requirements of this code provision.
There are thousands of FS boxes hanging around here in the labs of Silicon Valley.
