not sure if I understand your screws question.
the front cover/bezel is not screwed on at all (that's why you can take it off).
the PCB is screwed to the metal frame and the metal frame is screwed to the back cover.
all other parts (display and front bezel and IR fins) are held together by glue and glue alone. other kobo models (before waterproof/glue came along) just used clamps in the plastic frame itself (the kind as breaks off when you open it)
first picture here shows the device just before screwing it back onto the back cover.
I have to be a careful with mine since I didn't renew the glue pads for the display at all (they were not included in the package, unfortunately) so it probably doesn't stick very well anymore.
I considered buying another fintie case where the H2O just snaps in, but they seem to be out of stock indefinitely ... well, it is an older model
edit: oooh, I think maybe you were confused by my pictures that show how the front bezel hooks into the PCB? those were taken with out the back cover. that's just to understand what is happening / for illustration, not how you actually assemble it. you have to screw the unit into the back cover then put the front bezel on it (and can't see whether it went in properly, but it helps to know that this could be a problem, so wiggle things a bit until touch works). this device can only be opened from the front, order cannot change