NAC (Standard) Air Through Shaft Clutches 
NAC-type (standard) Pneumatic-Coaxial Pneumatic clutch is linked with air pressure on, and restoration relying on spring to open up.
Disc relies on air pressure to slide along the direction of the axis, contacting the friction plate. Disc, the friction board and so on, are assembling to the wheel to  come into a integrated structure. Friction plate can be parted by screwing nuts.