Today I disassembled the M21C and got some measurements of the reflector + glass that a fellow member requested via PM.
Keep in mind that I don't have a set of calipers, so I used a regular ruler to get the dimensions (so there's a margin for error).
Reflector's base diameter: 26mm
Reflector's top diameter: 45mm
Reflector's height: 39mm
Glass thickness: 2mm
Glass diameter: 50mm
And here's some photos of the glass and reflector:
