The most stretched phrase in the clutch world is HEAVY DUTY. For some models of vehicle we have 5 levels of Heavy Duty available.
The Direct Clutch Heavy Duty clutch kit, commonly sees a 15-20% increase in clamping force. This in most cases does not result in a firmer pedal, as this is due to still utilizing the stock diaphragm, with the increase in clamping force coming from a geometry change made inside the pressure plate, after it's completely dismantled and modified. While apart we often also grind the surface of the casting. This not only makes sure the surface is completely flat, but also gives the surface a cross hatch type finish, aiding in speeding up of the clutch run in period and ultimately holding more torque straight out of the box. We sometimes call these levels of modification Level 2 HD.
We can also offer further modification to the Heavy Duty (level 2) spec, via a diaphragm change, which sees a higher camping force, i.e. 25-40% increase, this we call the Direct Clutch Hi Torque or Level 3.
In many cases we can offer the High Torque (HT) Level 3 pressure plate and combine it with a higher temp / harder compound disc. Often called Level 4 or the Super Hi Torque.
Last in the Organic range, Level 5 comprises of a complete new flywheel allowing for a superior clutch to bolt to it. This new set up often comprises of a larger diameter clutch, higher clamping force.
*Photo is for illustration purposes only