screw.scad

$fs=$preview ? 1 : 0.1;  // Don't generate smaller facets than 0.1 mm
$fa=$preview ? 15 : 5;    // Don't generate larger angles than 5 degrees
screw_height = 20;
screw_radius = 10;
screw_pos_neg_offset = 1;
screw_pos_neg_ratio = (screw_pos_neg_offset + screw_radius) / screw_radius;
module bolt() {
    linear_extrude(
        height = screw_height,
        twist = screw_height * 20,
        slices = screw_height * 5
    ) {
            circle(r=screw_radius, $fn=6);
    }
}
module nut() {
    difference() {
        linear_extrude(height = screw_height) {
           circle(r=screw_radius * 1.5, $fn=6);
        }
        scale([screw_pos_neg_ratio, screw_pos_neg_ratio, 1]) bolt();
    }
}
bolt();
color("#ffff0022") nut();