Make your 0.4 3 header into 0.6..ive a cunning plan,said Baldrick.. 1st drill out nozzle to 0.6mm with these precision bits. 2nd measure E3D 0.6mm nozzle face dimensions. 3rd double sided tape 1200grit wet n dry to bed so its perfectly flat..having built 3 head carrige..use the z 0.01 function and the x/y to sand the tip face to same dimensions as an E3D 0.6 nozzle. Here is pic of Geeetech 0.4 straight out the box magnified using Swiss Army knife x10 eyeglass.Not quite central ; ( Any and all feedback + or - much appreciated.