Pat Lawrence
Amazing how something as simple as frozen water starts such a lengthy discussion. Pea-sized hail and sleet are nearly one in the same. As rdewey (and me) said the difference is in the way the two form---but they are made of the same thing, frozen water! Even the size of the two mentioned is very nearly identical 
Pat
Ps I noticed this definition in the online AMS glossary:
ice pellets- They may be spherical, irregular, or (rarely) conical in shape. Ice pellets usually bounce when hitting hard ground and make a sound upon impact. Now internationally recognized, ice pellets includes two basically different types of precipitation, known in the United States as 1) sleet and 2) small hail.
I didn't include the differences in formation which all of us probably already know.

Pat
Ps I noticed this definition in the online AMS glossary:
ice pellets- They may be spherical, irregular, or (rarely) conical in shape. Ice pellets usually bounce when hitting hard ground and make a sound upon impact. Now internationally recognized, ice pellets includes two basically different types of precipitation, known in the United States as 1) sleet and 2) small hail.
I didn't include the differences in formation which all of us probably already know.