The only noticeable difference I can find between the Mk10B and the Mk10C is the holes drilled on the side for the boom mic.
I believe these helmets use the Alpha 200 Helmet shell. They come with visor fairings to stop parachute risers getting caught in the visor levers.
There are oxygen mask bases attached to allow the use of MQR (Mask Quick Release) receivers or oxygen mask hooks.
