Although not limited to@ these clutches are normally used on trucks considered as Medium-Duty (Class 6 and 7)@ as well as Heavy-Duty (Class 8). Purpose??This SAE Recommended Practice specifies clutch dimensions to promote standardization of single-plate and two-plate pull type clutches. This includes flat and pot type clutches sized from 350 (14) to 430 (16.9). (See Figures 1 to 6.)