In these, the leading edge is sharp and free of burrs and the cylindrical section of the orifice is short, either because the entire plate is thin or because the downstream edge of the plate is bevelled. Exceptions include the quarter-circle or quadrant-edge orifice, which has a fully rounded leading edge and no cylindrical section, and the conical inlet or conical entrance plate which has a bevelled leading edge and a very short cylindrical section. The orifices are normally concentric with the pipe (the eccentric orifice is a specific exception) and circular (except in the specific case of the segmental or chord orifice, in which the plate obstructs just a segment of the pipe).