With the piece from the image 4 and this, we can get the focal lenght that we need for a 0.3 mms hole.
There are several tables in internet about this matter. The one that I follow specify 55mms distance from the film (the sensor in this case) to the hole.
The piece from the image 4 is a cap for the camera body when this is without lens.
The piece in this image is a water diffusor for a tap (only the external part).

In a Canon body the distance from the sensor to the seat of the lens is 40mms. The part 4 is 5mms high and the part 5 is 10 mms high. The result is ok (40+5+10=55).