An improved circle mounting bar and circle assembly for a motor grader includes a beam with a connecting end, and integral with the other end of the beam is a circle carrying structure in which an annular upright wall with an outwardly extending integral top flange and a removable bottom flange forms an outwardly open annular cavity. The circle structure is rotatably mounted between the flanges and cooperates with the wall and flanges to form a closed annular chamber which is sealed by circumferential seals, and an internal ring gear is on the circle structure in the cavity. An opening in the upright wall toward the beam accommodates an input drive element that engages the ring gear, and in that area the upright wall is the outer wall of a sealed housing that houses the input element and also contains lubricant for said element and the ring gear.