Airflex Expanding Clutches & Brakes utilize a rugged tire-like neoprene and cord tube that expands radially outward when pressurized.  The expanding tube forces a friction surface against an inner cylindrical drum surface.  The rate at which the tube is pressurized determines the rate at which element torque increases.  Final tube pressure and rotating speed determines the element torque capacity.

Product Sizing
Expanding elements are identified by the inside drum diameter in inches to which they expand and the width in inches of their friction lining. For instance, a size 16E475 is designed to expand to a 16 inch diameter drum and has a friction lining width of 4.75 inches.