This item should be sold with an included soft rubber base; otherwise it doesn't contour to the body panel.
I needed to apply black silicone deliberately to remedy the gap left between the base and the car's panel.
Also, the bolt used has a "square" end (with a gasket -good) but it makes the drilling of the of the panel to fit the bolt inadequate, as the drilling is obviously circular!! So, not as easy a bolt-on as it should have been.
In terms of signal reception, no noticeable improvement over the old rusty aerial it replaced.
My final verdict, it is mostly a "look" thing, but i was really torn about even mounting it once i saw what i was dealing with...