没找到合适的配件，只能自己做了。

difference(){union(){cylinder(11.5,10,10,$fn=365);translate([-10,0,0])cube([20,16,11.5]);rotate([0,90,0])translate([-11.5/2,16-3-2,-18])cylinder(20+8+8,3,3,$fn=365);}translate([0,0,-1])cylinder(13,2.5,2.5,$fn=365);
}