Summary

I made this because I had areas in my house that were to small for a standard box.
One style you can just snap the tab for inserting the wire.
The other one you can insert the adapter for inserting the wires.
The adapter plugs I got a Home Depot. Other stores probably have these. They are 1/2 inch

Single box - Inside 1.4W x 2.9H x 1.8D
Hole needed for box - 3.73H x 1.4W
Double box 1.4W x 2.9H x 1.8D
Hole needed for box - 3.73H x 3.4W