aggregate_el_size = 0.1;
paste_el_size = 0.1;
aggregate_radius = 0.016;
box_size = 0.0728; // this is the edge length of the box

Point(1) = {0, 0, 0, aggregate_el_size};
Point(2) = {aggregate_radius, 0, 0, aggregate_el_size};
Point(3) = {0, aggregate_radius, 0, aggregate_el_size};
Point(4) = {-aggregate_radius, 0, 0, aggregate_el_size};
Point(5) = {0, -aggregate_radius, 0, aggregate_el_size};

Point(6) = {box_size/2, box_size/2, 0, paste_el_size};
Point(7) = {-box_size/2, box_size/2, 0, paste_el_size};
Point(8) = {-box_size/2, -box_size/2, 0, paste_el_size};
Point(9) = {box_size/2, -box_size/2, 0, paste_el_size};
Point(10) = {0, -box_size/2, 0, paste_el_size};
Point(11) = {0, box_size/2, 0, paste_el_size};
Circle(1) = {2, 1, 3};
Circle(2) = {3, 1, 4};
Circle(3) = {4, 1, 5};
Circle(4) = {5, 1, 2};
Line(9) = {9, 6};
Line(10) = {6, 11};
Line(11) = {11, 7};
Line(12) = {7, 8};
Line(13) = {8, 10};
Line(14) = {10, 9};
Line Loop(13) = {4, 1, 2, 3};
Plane Surface(14) = {13};
Line Loop(17) = {9, 10, 11, 12, 13, 14};
Plane Surface(18) = {17, 13};
Physical Surface("aggregate") = {14};
Physical Surface("paste") = {18};
Physical Line("bottom") = {13, 14};
Physical Line("right") = {9};
Physical Line("top") = {10, 11};
Physical Line("left") = {12};
Physical Point("top_center") = {10};
Physical Point("bottom_center") = {11};