George,
I went to measure mine for you, but even with the garage lights on there was not enough light to see it under the car. I will measure it when I get a chance and the light is better. Mine did not have the plugs in so I could not tell you if was rubber or plastic. You are talking about the ones behind the rear tires on the inside of the qtr with the little drip hole below the round hole, and not the one in the inner wheel well cover correct?