,
The OEM clutch cover uses these crimped tabs to hold the diaphragm spring in place. This is both weak and loses some efficiency as the spring isn't fastened around its entire perimeter allowing flex between the mounting points. 
The ACT clutch cover rivets the diaphragm spring directly to the top of the cover allowing the diaphragm spring to flex as the clutch is engaged and disengaged. You can see the holes for the rivets around the top of the cover here. Not only is this stronger and stiffer than the folded tab retention method but it also supports the spring better which improves efficiency.
Here are the headed rivets. These fasten the diaphragm spring to the clutch cover while still allowing the spring to float enough to bend and pivot.
Here is the assembled pressure plate with everything riveted together. 
Here is the forged one piece chromoly Streetlite flywheel. Forging makes for a stronger more ductile part due to grain alignment and refinement developed in the forging process. Superior materials and manufacturing methods allow the flywheel to be 5.7 lbs lighter than stock. Note that the pilot bearing is retained in the flywheel rather than in the crankshaft. 
