module hook(diameter, length_rest, length_slide, angle=45) {
  angle = 30;
  rotate([-90, 0, 0])
  cylinder(r=diameter/2, h=length_rest, $fs=0.1);

  translate([0, length_rest, 0])
  rotate([angle, 0, 0])
  hull() {
    translate([0, length_slide, 0])
    sphere(diameter/2, $fs=0.1);

    sphere(diameter/2, $fs=0.1);
  }
}

hook(5, 20, 10);