A simple lockpick, untested

lockpick-template-taper-thintip.scad

translate([0,4])
{
    translate([-20,0])
    {
        square(size=[40,8], center=true);
    }
    
    translate([0,0])
    {
        circle(r=4);
    }
    
    translate([3,-1])
    {
        // overflows 1 unit into left object
        polygon_wide_size = 2; // taken from pick
        polygon_narrow_size = 1.3; // taken from pick
        size_difference = (polygon_wide_size - polygon_narrow_size);
        half_size_difference = size_difference / 2; // half on top, half on bottom
        polygon_narrow_top = polygon_narrow_size + half_size_difference;
        polygon_narrow_btm = half_size_difference;
        
        polygon(points=[
            [0,0],
            [21,polygon_narrow_btm],
            [21,polygon_narrow_top],
            [0,2]
        ]); 
        
        // add a 20mm custom end - you can add other ends in this section
        
        // cutout circle section with some features
        translate([21,-1*(polygon_narrow_size+polygon_narrow_btm)])
        {
            outer_circle = 2* (polygon_narrow_btm + polygon_narrow_size);
            inner_circle = 2*polygon_narrow_btm + polygon_narrow_size;
            tip_circle = (outer_circle - inner_circle) / 2;
            difference()
            {
                // keep the top right quarter of the circle...
                intersection()
                {
                    circle(r=outer_circle, $fn=500);
                    // this translate can be deleted
                    translate([0,0])
                    {
                        square([outer_circle, outer_circle]);
                    }
                }
                circle(r=inner_circle, $fn=500);
            }
            translate([outer_circle-tip_circle, 0])
            {
                circle(r=tip_circle, $fn=500);
            }
        }
    }
}