Plastic Bushing Rated for Inside the Main Panel?

I am trying to determine whether or not plastic bushings are rated to securing wiring inside the main electrical panel. Could somebody help me determine where to find more information. Thank you!

Can you be more specific as to how the plastic bushing is securing the wiring?

Why do you think the panel would need a different connector than a junction box?

Bushing are used to provide a smooth edge. They do not secure a cable to the panel or box.

There are some bushing that have an additional grounding connector where they are serving a transfer box application. The conduit is primarily used to ensure grounding between any junction boxes or additional panels.