MSA Millennium Speaking Diaphragm cover

This is an adapter and detail piece designed to thread into the retaining ring (part 6 on the exploded diagram) on the front of a MSA Millenium Gas mask. It's open to allow the speaking diaphragm to function normally.
I've included two different 'inserts' that you can use, or you can mix your own! There are grooves to accept the inserts on both the front and rear of the threaded portion.

I designed this to go with this set of prints from an amazing artist Lukas who designed a complete sci-fi helmet addition to the normal MSA millennium mask. The files are for sale here: https://carbon-cats.gumroad.com/l/headshield (I get no compensation for this, I just think it's awesome.)
Warning! Some (a lot) of their artwork is NSFW, but this particular link should be SFW.

If you want to install this -in place of- the existing diaphragm (#7) and retaining ring (#6), you will need to scale everything up 102% in the X and Y, but NOT the Z. You'll need some sort of pin spanner to remove the retaining ring. Or you can do what I did and put two nails in a block the correct distance apart (3d printed specialty tool: $0.05, commercial tool: $15-$90+!) and unscrew it carefully.
Support material is minimal if the adapter is printed face down. The inserts shouldn't require any supports at all if printed flat on their back.
The insert outer diameter by default is 45mm, Insert 1 is 3mm thick, the hex grid insert is 0.5mm thick and the groove in the adapter has a 1mm wide surface to glue the inserts to.
Both front and rear grooves are 3mm deep, so if you're just using insert 1 it will sit flush with the front. 
I recommend threading the adapter ring into place and then 'snap fitting' the insert into the groove to ensure the alignment is to your liking before you glue the insert in place with the glue of your choosing.
Personally I printed these in ABS, so I just used some acetone to bond the parts together.