bare-low/o4-mini / tier-3-butt-hinge

```openscad
// OpenSCAD code for a small butt hinge (180° open)

$fn = 64;

// Parameters
leaf_length = 30;    // along Y
leaf_width  = 25;    // along X from hinge axis
leaf_thick  = 2;
knuckle_od  = 8;
knuckle_id  = 4.6;
knuckle_h   = leaf_thick;
knuckle_pitch = leaf_length/5; // 6mm
pin_d       = 4;
pin_len     = leaf_length + 2; // 32mm
csk_d       = 6;
csk_depth   = 1;
hole_d      = 3.2;
hole_pitch  = 8;

// Leaf module: side = -1 for left, +1 for right
module leaf(side = 1) {
    // Board
    translate([ (side==1?0: -leaf_width), -leaf_length/2, 0 ])
        cube([leaf_width, leaf_length, leaf_thick]);
    // Knuckles
    yoffs = [-12, -6, 0, 6, 12];
    for (i = [0:4]) {
        use = (side==-1 && (i==0 || i==2 || i==4)) || (side==1 && (i==1 || i==3));
        if (use) {
            translate([0, yoffs[i], 0])
                knuckle();
        }
    }
    // Countersunk holes on far edge
    for (i=[-1,0,1]) {
        y = i * hole_pitch;
        x = side==1 ? leaf_width : -leaf_width;
        // Through hole
        translate([x, y, 0])
            rotate([90,0,0])
            cylinder(d=hole_d, h=leaf_thick+1, center=true);
        // Countersink (subtractive)
        translate([x, y, leaf_thick - csk_depth])
            rotate([90,0,0])
            cylinder(h=csk_depth, r1=csk_d/2, r2=hole_d/2, center=false);
    }
}

// Knuckle as hollow cylinder
module knuckle() {
    difference() {
        cylinder(d=knuckle_od, h=knuckle_h, center=false);
        translate([0,0,0])
            cylinder(d=knuckle_id, h=knuckle_h+0.1, center=false);
    }
}

// Pin
module pin() {
    translate([0, 0, leaf_thick/2])
        rotate([0,0,0])
        cylinder(d=pin_d, h=pin_len, center=true);
}

// Assemble
leaf(-1);
leaf(1);
pin();
```