The “maximum size” is the smallest sleve opening which all of the aggregates will pass.  The “nominal maximum size” is the smallest sleve opening in which of most of the aggregate will pass.

 

For example, #57 coarse aggregate has a nominal maximum size of 1” since most (over 95%) of the material will pass through a 1” sleve.  However, #57 coarse aggregate has a maximum size of  1½” since all of the material must pass through a 1 ½” sleve although  through a small part (less than 5%) may be retained in the 1” sleve.

 

 

 

 

 

 

 

 

 

 

The distinction can become very important when analyzing specifications and test methods.