radiusT = 50;
radiusF = 7;
diameterF = radiusF * 2 - 2;
offsetC = 6;
offsetF = 2;


difference()
{
    circle(radiusT, $fn = 3);
    circle(radiusT - offsetC, $fn = 3);
}


for(i = [
    [diameterF * 2, diameterF / 2], 
    [diameterF * 2, -diameterF / 2], 
    [diameterF * 3, 0], 
    [diameterF, diameterF], 
    [diameterF, 0], 
    [-diameterF, 0], 
    [0, diameterF], 
    [0, 0], 
    [0, -diameterF],
    [-diameterF/2, diameterF * 2],
    [-diameterF/2, -diameterF * 2],
    [-diameterF, -diameterF],
    [-diameterF, diameterF],
    [diameterF, -diameterF]])
{
    translate(i)
    difference()
    {
        circle(radiusF, $fn = 128);
        circle(radiusF - offsetF, $fn = 128);
    }
}