bare/gpt-oss-120b / tier-3-butt-hinge

```openscad
$fn = 64;

//-------------------------------------------------
// Parameters
leaf_thick = 2;
leaf_len   = 30;
leaf_wid   = 25;

knuckle_len = 6;
knuckle_out_r = 4;
knuckle_in_r  = 2.3; // pin radius 2 + 0.3 clearance

pin_r   = 2;
pin_len = 32;

hole_dia_top = 6;   // countersink top diameter
hole_dia_bot = 3.2; // through hole diameter
hole_depth   = 1;   // countersink depth
hole_pitch   = 8;
hole_ys = [6, 14, 22]; // positions for three holes

//-------------------------------------------------
// Helper modules
module knuckle(yc) {
    // tube (outer - inner) centered at X=0, Z=0, Y=yc
    translate([0, yc, 0])
        rotate([90,0,0])
            difference() {
                cylinder(r=knuckle_out_r, h=knuckle_len, center=true);
                cylinder(r=knuckle_in_r,  h=knuckle_len, center=true);
            }
}

module countersink_hole(yc, side="left") {
    // side = "left"  -> X negative outward
    // side = "right" -> X positive outward
    sign = (side=="left") ? -1 : 1;
    // countersink cone (base on leaf surface)
    translate([sign*(leaf_thick/2 + hole_depth), yc, 0])
        rotate([0,90,0])
            cylinder(r1=hole_dia_top/2, r2=hole_dia_bot/2, h=hole_depth, center=false);
    // through hole cylinder
    translate([sign*(leaf_thick/2), yc, 0])
        rotate([0,90,0])
            cylinder(r=hole_dia_bot/2, h=leaf_thick+0.01, center=true);
}

//-------------------------------------------------
// Leaf definition
module leaf(side="left") {
    sign = (side=="left") ? -1 : 1;
    // Main block
    block = translate([sign*leaf_thick, 0, -leaf_wid/2])
                cube([leaf_thick, leaf_len, leaf_wid], center=false);
    // Knuckles (interleaved)
    knuckles = [];
    if (side=="left") {
        // sections 0,2,4  -> centers 3,15,27
        knuckles = [3, 15, 27];
    } else {
        // sections 1,3 -> centers 9,21
        knuckles = [9, 21];
    }
    // Build leaf with knuckles
    leaf_union = union() {
        block;
        for (yc = knuckles) knuckle(yc);
    }
    // Subtract countersink holes on outer side
    for (yh = hole_ys)
        difference() {
            leaf_union;
            countersink_hole(yh, side);
        }
    // The above loop would overwrite leaf_union each iteration,
    // so we instead apply subtraction in a single difference:
    difference() {
        leaf_union;
        for (yh = hole_ys)
            countersink_hole(yh, side);
    }
}

//-------------------------------------------------
// Pin definition
module pin() {
    // Pin centered in Y at leaf midpoint, extends 1mm beyond each leaf end
    translate([0, leaf_len/2, 0])
        rotate([90,0,0])
            cylinder(r=pin_r, h=pin_len, center=true);
}

//-------------------------------------------------
// Assembly
union() {
    // Left leaf (x negative side)
    leaf("left");
    // Right leaf (x positive side)
    leaf("right");
    // Pin
    pin();
}
```