In Q8, PMS SEND TO THOSE WITH ISSUES BLF soda can light - #12509 by Tom_Tom Etex measured the brass ring at 1/16” thick, i.e. 1.59 mm
See e.g. http://fastener-express.com/fastener-technical/Metmachpanhd.pdf for standard dimensions of metric phillips pan-head screws, dimension H1 applies (maximum).
E.g. 1.60 mm max for an M2 screw, or 2.1 mm for M2.5. Which size is used ? Both of these would be proud of the brass ring.
Once you get to M2.5, H1 minimum is 1.96mm, i.e. guaranteed to be proud.
At M2.0 H1 min is 1.46 mm (only 0.13mm clearance), but at the mean, 1.53 mm, there is only 0.06mm clearance.
This assumes good quality screws complying to spec.
Not acceptable at-all.
You’d have to go down to an M1.6 pan head screw to be sure of being under-flush. By only 0.3 mm. Which is a tiny screw.
It’s called tolerance analysis. Chances are most screws will be somewhere less than maximum, so with an M2 screw you might not see it, even if you looked for it, on a prototype.
And it would never be an issue using a button-top, inserted the correct way round.
But a designer should also consider possible real-life fault scenarios, and take steps to mitigate them, where reasonably practical. Designing reverse-polarity protection rings, prototyping them, but then removing them for production puzzles me.
