iter-png-3/gemini-2.5-flash / tier-2-hex-bolt

```openscad
// M8 Hex Bolt

// Dimensions for the M8 hex bolt
// Standard dimensions for M8 bolts (ISO 4017/DIN 933 or similar)
// Head across-flats (s): 13 mm
// Head height (k): 5.3 mm
// Shank diameter (nominal thread diameter, d): 8 mm
// Shank length (l): 30 mm

// --- Parameters ---
// Head dimensions
head_across_flats = 13;   // 対辺距離 (across-flats)
head_height = 5.3;        // 頭部の高さ

// Shank dimensions
shank_diameter = 8;       // シャンクの直径
shank_length = 30;        // シャンクの長さ

// --- Calculated values ---
// Radius of the circumcircle for the hexagonal head
// For a regular hexagon, the across-flats distance (s) is related to the circumcircle radius (R) by:
// s = 2 * R * cos(30 degrees)
// R = s / (2 * cos(30 degrees)) = s / sqrt(3)
head_radius_circumcircle = head_across_flats / sqrt(3);

// Shank radius
shank_radius = shank_diameter / 2;


// --- Bolt Assembly ---
union() {
    // 1. Hexagonal Head
    // Placed such that its bottom face is at z=0 and extends upwards (+Z direction).
    // $fn=6 specifies a hexagon (6 faces).
    // center=false makes the cylinder extend from z=0 to z=height.
    cylinder(
        h = head_height,
        r = head_radius_circumcircle,
        $fn = 6,
        center = false
    );

    // 2. Shank (Cylindrical part)
    // Placed such that it starts from z=0 and extends downwards (-Z direction).
    // The cylinder itself is defined from z=0 to z=shank_length (center=false).
    // It is then translated downwards by its full length to align its top face with z=0.
    translate([0, 0, -shank_length])
    cylinder(
        h = shank_length,
        r = shank_radius,
        center = false
    );
}
```