// Twist.
linear_extrude(
    height = 10,
    center = false,
    convexity = 10,
    twist = 360,
    $fn = 100
)
translate([2, 0, 0])
circle(r = 1);

// Torus.
translate([0, 5, 2])
rotate_extrude(convexity = 10, $fn = 100)
translate([2, 0, 0])
circle(r = 1, $fn = 100);

// Hook.
translate([0, 5, 8])
rotate([90, 0, -90])
scale(0.02)
union () {
    translate([0,60,0])
       rotate_extrude(angle=270, convexity=10)
           translate([40, 0]) circle(10);
    rotate_extrude(angle=90, convexity=10)
       translate([20, 0]) circle(10);
    translate([20,0,0]) 
       rotate([90,0,0]) cylinder(r=10,h=80);
}