Diameter = 101.6; // 0.1
Depth = 6; // 0.1

Inset = false;
Inset_depth = 4; // 0.1
Inset_width = 5; // 0.1

Inner_pattern = "n"; // [n: None, c: Circle]
Inner_pattern_width = 5; // 0.1
Inner_pattern_depth = 1; // 0.1

$fn = 180; // 0.1

module coaster_frame() {
difference() {
cylinder(h = Depth, d = Diameter); 
if (Inset) {
    cylinder(h = Inset_depth, d = Diameter - 2*Inset_width);
};
};
}

module coaster_pattern() {
  offset = Inset ? [0, 0, Inset_depth - Inner_pattern_depth] : [0, 0, -Inner_pattern_depth];
  if (Inner_pattern == "c") {
    translate(offset) {
     #cylinder(h = Inner_pattern_depth, d = Inner_pattern_width);
    }
  }    
}

rotate([0, 180, 0]) {
  union() {
    coaster_frame();
    coaster_pattern();
  }
};