hole_dia = 14;
hole_depth = 29;

wall_thickness = 3;

screw_hole_dia = 4;
screw_hole_chamfer = 2;

module slot(width, height) {
    radius = width / 2;
    squ_height = height-2*radius;

    union(){
        square(size=[width, squ_height], center=true);
        translate([0,squ_height/2,0])
        circle(r=radius);
        translate([0,-squ_height/2,0])
        circle(r=radius);
    }
}

module sector(radius, angles, fn = 24) {
    r = radius / cos(180 / fn);
    step = -360 / fn;

    points = concat([[0, 0]],
        [for(a = [angles[0] : step : angles[1] - 360]) 
            [r * cos(a), r * sin(a)]
        ],
        [[r * cos(angles[1]), r * sin(angles[1])]]
    );

    difference() {
        circle(radius, $fn = fn);
        polygon(points);
    }
}

module holder() {
    inner_radius = 10.5;
    round_radius = 3;


    minkowski() {
        difference(){
            circle(r=inner_radius+round_radius+0.1);
            circle(r=inner_radius+round_radius);
            sector(inner_radius+round_radius+2, [-30, 210]);
        }
        circle(r=round_radius, $fn=25);
    }
}

module safety() {

}

linear_extrude(wall_thickness){
    slot(30, 60);
}

my_offset = -13;

translate([0,my_offset,wall_thickness])
linear_extrude(wall_thickness)
holder($fn=100);

color("lavender") {
    translate([0,my_offset,4])
    circle(r=10);
}