iter-png-1/gpt-5.4-mini / tier-2-hex-bolt

```openscad
$fn = 64;

module m8_hex_bolt() {
    union() {
        // Head: hexagonal prism, across-flats 13mm, height 5.3mm
        // In OpenSCAD, cylinder(..., $fn=6) is inscribed in the circumscribed circle,
        // so the radius must be set from across-flats.
        translate([0, 0, 0])
            cylinder(h = 5.3, r = 13 / (2 * cos(30)), $fn = 6);

        // Shank: cylindrical shaft, diameter 8mm, length 30mm
        // Head bottom at z=0, shank extends toward negative Z.
        translate([0, 0, -30])
            cylinder(h = 30, d = 8);
    }
}

m8_hex_bolt();
```