Small pieces that are part of a bigger piece.
Subfragments are usually tiny and not very important on their own.
Examples:
I found subfragments of the broken plate on the floor.
The scientist studied the subfragments of the ancient pottery.
She collected the subfragments of the shattered vase.
The detective used the subfragments of the torn paper to solve the case.
The archaeologist discovered tiny subfragments of the ancient statue.
The artist used the subfragments of glass to make a beautiful mosaic.