iter-png-3/gpt-5.4-mini / tier-3-butt-hinge

```openscad
$fn = 96;

// Base dimensions
leaf_len = 30;          // along Y
leaf_w   = 25;          // along X
leaf_th  = 2;           // along Z

pin_d    = 4;
pin_len  = 32;          // extends 1mm beyond knuckles at both ends

knuckle_od = 8;
knuckle_id = 4.6;
knuckle_len = 6;        // 30mm / 5

m3_through_d = 3.2;
m3_csk_top_d = 6;
m3_csk_depth = 1;

// Open 180° layout:
// leaves are coplanar in Z, and separated on X so their free edges point away
// from the hinge axis. Hinge axis is along Y at X=0.
left_leaf_center_x  = -(pin_len/2 + leaf_w/2);
right_leaf_center_x =  (pin_len/2 + leaf_w/2);

left_knuckle_y  = [-12, 0, 12];   // 3 segments: 1,3,5
right_knuckle_y = [-6, 6];        // 2 segments: 2,4

// M3 holes: 3 per leaf, spaced 8mm along Y, on the side away from knuckles.
hole_y = [-8, 0, 8];

module leaf_plate(side = -1) {
    translate([side * (pin_len/2 + leaf_w/2), 0, 0])
        cube([leaf_w, leaf_len, leaf_th], center=true);
}

module knuckle_segment(yc) {
    translate([0, yc, 0])
    difference() {
        cylinder(d=knuckle_od, h=knuckle_len, center=true);
        cylinder(d=knuckle_id, h=knuckle_len + 2, center=true);
    }
}

module pin_axis() {
    rotate([90, 0, 0])
        cylinder(d=pin_d, h=pin_len, center=true);
}

module leaf_with_knuckles(side = -1) {
    leaf_x = side < 0 ? left_leaf_center_x : right_leaf_center_x;
    knuckles = side < 0 ? left_knuckle_y : right_knuckle_y;
    hole_x = side < 0 ? (leaf_x + leaf_w/2 - 0.8) : (leaf_x - leaf_w/2 + 0.8);
    csk_dir = side < 0 ? 1 : -1;

    difference() {
        union() {
            translate([leaf_x, 0, 0])
                cube([leaf_w, leaf_len, leaf_th], center=true);

            for (yy = knuckles)
                knuckle_segment(yy);
        }

        // Through holes
        for (yy = hole_y) {
            translate([hole_x, yy, 0])
                rotate([0, 90, 0])
                    cylinder(d=m3_through_d, h=leaf_w + 2, center=true);

            // Countersink from the outer face of the leaf
            translate([leaf_x + csk_dir * leaf_w/2, yy, 0])
                rotate([0, 90, 0])
                    cylinder(d1=m3_csk_top_d, d2=m3_through_d, h=m3_csk_depth, center=false);
        }
    }
}

union() {
    leaf_with_knuckles(-1);
    leaf_with_knuckles(+1);
    pin_axis();
}
```