// parameters
lc = 0.01;
lx = 0.01;
lz = 0.1;
// we define a delta gap
delta_gap = lz/2.0; // length of delta gap

// and now the geometry
Point(1) = {0, 0, 0, lc};
Point(2) = {-lx, 0, 0, lc};
Point(3) = {0, -lx, 0, lc};
Point(4) = {lx, 0, 0, lc};
Point(5) = {0, lx, 0, lc};
Circle(1) = {2,1,3};
Circle(2) = {3,1,4};
Circle(3) = {4,1,5};
Circle(4) = {5,1,2};
Line Loop(5) = {3,4,1,2};
Plane Surface(6) = {5};
Extrude {0,0,delta_gap/2.0} {
  Surface{6};
}
Extrude {0,0,-delta_gap/2.0} {
  Surface{6};
}
Extrude {0,0,lz-delta_gap/2.0} {
  Surface{28};
}
Extrude {0,0,-lz+delta_gap/2.0} {
  Surface{50};
}