preferably cap 20 comprises two regions top region 22 and middle region 24 top region 22 extends across the cap from one side to another similarly bottom region 28 extends from the based of the cap from one side to the other outer edge 34 joins from one side of top region 22 and middle region 24 to form a curve and then joins the other side of top region 22 and middle region 24 and together form a generally mushroom shape cap structure preferably outer edge 34 connects with top region 22 to form an arch to form an ellipse shape with first radius 26 then outer edge 34 preferably curves downward to connect with middle region 24 to form another ellipse with second radius 28 the downward curves allow for a mushroom cap like shape which also preferably means that top radius 26 is greater than middle radius 28 generally a circle is defined by one point and the distance radius r however it is preferred that the arch formed by joining outer edge 34 with top region 22 and middle region 24 is of an ellipse the ellipse is a natural extension of the circle instead of having one.