here's some info i found 
Class A:     is required to drive combination vehicles, such as tractor-trailers, with a gross combination weight rating (GCWR) of 26,001 pounds or more, provided the vehicle being towed has a gross vehicle weight rating (GVWR) of 10,001 pounds or more.   
Class B:     is required to drive single vehicles with a GVWR of 26,001 or more pounds; the operator may tow a vehicle weighing 10,000 pounds GVWR or less.  
Class C:    is for cars, vans, pickups, mopeds, and other vehicles with a GVWR of 26,000 pounds or less; allows towing of a vehicle with a GVWR of 10,000 pounds or less.  
Class M:     is for motorcycles. If you drive a motorcycle and a Class A, B, or C vehicle, your license will show both classes, provided you have met all other requirements. Additionally, Nevada has a Class M license with a U Restriction that limits riders to mopeds, trimobiles, and motorcycles that are less than 90 cc and do not exceed 6½ horsepower.  
See Motorcycles, Mopeds & Bicycles.  
Endorsement J         Allows Class C license to tow a vehicle over 10,000 pounds GVWR.   
Additional written and skills tests are required.  
Endorsement R          Allows Class C license to tow a combination of vehicles not to exceed 70 feet in length. Additional written and skills tests are required.   
Endorsement  F   
See Nevada Administrative Code Chapter 483 for a complete list of restrictions.  
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