Abstract: The rolling mill plug assembly comprises a guide plug and a working plug joined together in interlocking relationship. The working plug includes a female connection formed by a socket recess in one end. Two opposing flanges extend over the recess and are spaced apart by a central opening and opposing slots in registry with the recess. The guide plug includes a male connection comprised of a neck extending outward from one end of the guide plug which terminates in two opposingly extending lugs which are adapted to pass through the slots and into the recess in the working plug. Rotating the guide plug positions the lugs under the flanges and locks the guide plug in place within the recess of the working plug. A key assembly can be employed with the two plugs to maintain them in interlocking relationship.