Looks like an outdoor junction box cover and the included gasket.What kind of gasket material did you use for the one outside? Looks like a black gasket of some type.
Correct on the outdoor round box, I have a Jig setup for the covers, I drill 2 holes for the cam holes and use the cover with a longer screw for the third cam hole and a hole in the middle for the wires, depending on the location I sometimes pop a small hole in the bottom for a moisture drain. I use the stock gasket that comes with the outdoor box and dab a little clear silicone around the top to keep the water out in case the gasket leaks.Looks like an outdoor junction box cover and the included gasket.