NOS Leviton 8300 from ebay ($~$6 each). I don’t know if the current 8300s are quite the same.
The recepticles are "back-fed"and there are two holes for each terminal (4 holes per side) with a jumper between the terminals. I used the deep boxes to allow more room to turn the wires. The case has a common ground.
The 8-gauge wire is multi-strand with 7 strands each. Strip the wire back, and separate it into a bundle of 3 and a bundle of 4 and push the two bundles into the two holes, where they easily fit (and could probably be multi-strand 6-gauge wire), and tighten down the side screws to secure the bundles.
Leave the jumper in place and from there, you can use the other two holes, again splitting the bundle to jump to the next recepticle. Code allows using these jumpers to pass the current.
The solid ground wire is a smaller gauge and can pass through the ground terminal lug on to the next recepticle without problem.
This is the NOS version, similar to what I have. Look at the back and you will see what I mean.