Abstract: A valve assembly includes a valve and a gearbox. The valve includes a valve body having a drive opening and a mounting surface adjacent the drive opening. At least one mounting bore is formed in the mounting surface. At least one rigid pin is fixed to and projects from the mounting surface. A rotatable valve member is disposed in the valve body. A gearbox is operable to rotate the valve member through the drive opening. The gearbox includes a casing including a mounting wall positioned adjacent the mounting surface of the valve body. At least one mounting hole is formed in the mounting wall and is disposed adjacent the mounting bore. At least one pin hole is formed in the mounting wall and receives the pin. A drive hole is formed in the mounting wall and communicates with the drive opening. At least one fastener extends through the mounting hole and engages the mounting bore to secure the casing to the mounting surface. The pin resists relative rotational movement of the casing and the valve body.