[Gmsh] How to make a hole in a volume?

[Toshiro K. Ohsumi]

Hello,

    I would like to put a hole in a volume, something like the magnetron in
the Gmsh gallery.  Unfortunately, it is not exactly clear from the tutorial
how to do this, either in a *.geom file or by the GUI.  (In the latter, I am
not sure how the hole specification works.)  I have created the points and
lines, as attached below.  What I need is the top and bottom surface (the area 
between the concentric surfaces), the four sizes, and the volume between the
outer walls and the inner walls.  Any tips on how to do this (e.g. an example
*.geom file) would be much appreciated.  Many thanks,



		- Toshiro K. Ohsumi

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Point(1) = {3.075,3.075,1,0.4};
Point(2) = {-3.075,3.075,1,0.4};
Point(3) = {-3.075,-3.075,1,0.4};
Point(4) = {3.075,-3.075,1,0.4};
Point(5) = {2,2,1,0.4};
Point(6) = {-2,2,1,0.4};
Point(7) = {-2,-2,1,0.4};
Point(8) = {2,-2,1,0.4};
Point(9) = {2,2,-1,0.4};
Point(10) = {-2,2,-1,0.4};
Point(11) = {-2,-2,-1,0.4};
Point(12) = {2,-2,-1,0.4};
Point(13) = {3.075,3.075,-1,0.4};
Point(14) = {-3.075,3.075,-1,0.4};
Point(15) = {-3.075,-3.075,-1,0.4};
Point(16) = {3.075,-3.075,-1,0.4};
Line(1) = {2,1};
Line(2) = {1,4};
Line(3) = {4,3};
Line(4) = {3,2};
Line(5) = {10,9};
Line(6) = {9,12};
Line(7) = {12,11};
Line(8) = {11,10};
Line(9) = {7,8};
Line(10) = {8,5};
Line(11) = {5,6};
Line(12) = {6,7};
Line(13) = {5,9};
Line(14) = {12,8};
Line(15) = {11,7};
Line(16) = {6,10};
Line(17) = {14,13};
Line(18) = {13,16};
Line(19) = {16,15};
Line(20) = {15,14};
Line(21) = {2,14};
Line(22) = {1,13};
Line(23) = {3,15};
Line(24) = {4,16};