Abstract: A camming device for centering a meter or other instrument having a cylindrical body with respect to the upstream and downstream pipes of a flow line in which the meter is interposed. Each pipe is provided with an end flange having a circle of bolt holes, the pipe flanges being bridged by clamping bolts which pass through the holes to encage and compress the meter, the holes having clearances allowing limited bolt play. Rotatably mounted on the meter body is a camming device provided with a symmetrical array of camming edges that tangentially engage the bolts. When the device is turned on the meter body, it acts to force the bolts to their extreme hole positions, as a result of which the meter body is caused to assume a position concentric with the bolt circle that is centered with respect to the pipes.