module screw(r=){

    for(g=[::]){

        translate([cos(g)*r,sin(g)*r,(g)/])

        rotate(a=[,,g])

        cylinder(.,.,.,center=true,$fn=);

    }

}

module ring(h,r1,r2){

    difference(){

        cylinder(h,r1,r1,$fn=);

        cylinder(h,r2,r2,$fn=);

    }

}

union(){

    // Cylinder shell

    difference(){

        cylinder(,16.5,16.5,$fn=);

        translate([,,])cylinder(,15.5,15.5,$fn=);

    }

    // Patterns on the shell

    for(i=[:0.2:]){

        rotate(i*/,[,,])

        translate([,16.5,])

        cylinder(,.,.,$fn=);

    }

    // Washer

    translate([,,])ring(,12.5,);

    translate([,,])ring(,14.5,);

    // Screw

    union(){

        translate([,,])screw();

        translate([,,])rotate([,,])screw();

        translate([,,])rotate([,,])screw();

    }

}