Differential Plug

Quick question, hoping to save a trip under the car. I want to make sure we have the right tool for taking out the bolt to check the gear oil level in the rear end. We have a 1969 Dart with the 7 1/4 pot. We changed out covers a while back, and are not sure that there is enough gear oil in there. We were told that the bold is a T30, but I would like to be sure before we run off to purchase it.

Thanks much in advance.

Nonie