Designed to handle heavy-duty antenna installations.  FireStik put a 5/8" hole in their aluminum mirror brackets to accommodate our DM-4A Dome Mount.  The DM-264A mount only has a groove in the clamp so it may be turned either horizontally or vertically and therefore allow for installation in either plane.  Optionally, the clamp may be omitted and the mount utilized as a side mount on any vertical surface.