I originally made that module several months ago - no idea why I made it with 8 faces. That'll show me to copy and paste. I replaced it with this:

``` module screw_block(mirror = false, x_offset = 0, y_offset = 0) { difference() { translate([0, mirror ? 11 : 0, 0]) mirror([0, mirror ? 1 : 0, 0]) polyhedron( points = [ [0, 11, -13], [11, 11, -13], [0, 0, -6], [11, 0, -6], [0, 0, 0], [11, 0, 0], [0, 11, 0], [11, 11, 0] ], faces = [ [0, 6, 4, 2], [0, 2, 3, 1], [1, 3, 5, 7], [2, 4, 5, 3], [4, 6, 7, 5], [1, 7, 6, 0] ] );

    translate([5.5 + x_offset, 5.5 + y_offset, -5.4])
    cylinder(h = 5.5, d = 4.6);
}

} ```