// -*- C -*-

circle_inner_rad = 10;

thick = 3;

tab_sz = 15;

// calculated

circle_outer_rad = circle_inner_rad + thick;

module Plan() {
  difference(){
    circle(r=circle_outer_rad);
    circle(r=circle_inner_rad);
    mirror([1,0]) square([50,50]);
  }
  translate([-circle_outer_rad, -0.1])
    square([thick, tab_sz + circle_outer_rad]);
}

Plan();