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The pressure ring is the part of the pressure plate that clamps down on the clutch disc. It is made of heat resistant nodular iron. The machined ridge on the backside of the pressure ring is the point where the diaphragm spring presses on the pressure ring. The location of this ridge, which contributes to peak clamp load and release efficiency, is what determines the leverage ratio of the diaphragm spring. If it is positioned inward, the diaphragm spring has more leverage, giving more clamp load and a longer engagement travel. If it is moved outward, there is less clamp load and a shorter engagement travel.
The ACT pressure ring is larger in diameter to accommodate the application's larger than stock clutch disc. The ACT disc is 240mm in diameter vs the stock 230mm diameter. The ACT disc has a lot more surface area than stock for more holding power and increased durability. 
Here are all the pressure plate components ready to be assembled. Every single ACT component in the pressure plate assembly is beefed up over the standard OEM part. 
The drive straps attach the pressure ring to the clutch cover. Their job is to transfer the engine's torque from the clutch cover which is bolted to the flywheel to the pressure ring. They also retract the pressure ring from the disc when the clutch pedal is pushed in.It is hard to believe that these little thin sheet metal pieces carry the engine's torque but they do. ACT triples them up so you have way more strength here than your typical stock parts.
These metal rings are the fulcrums that the diaphragm spring pivots on when you push the clutch pedal in. One is on top of the diaphragm spring the other is on the bottom. The pivot points of the diaphragm spring are the ridge on the pressure ring, the wire fulcrum rings and the throwout bearing.
These beefy rivets attach the drive straps to the pressure ring on one end and the clutch cover at the other.
