I looked at page 4 of the UL document here:
And I notice that it says you can use up to 4 #12 wires. However, it doesn't specify stranded or solid. I assume either and/or both is okay?
My plan is to push through 1 12AWG solid wire from the outlet ground screw through the connector to the box ground screw, then join in 2 12AWG stranded ground wires passing thru the box. Three wires total in the connector This is a 20A receptacle on a 20A breaker in a metal box with EMT conduit.