Weigh them or measure them! Brightly colored interlocking plastic cubes each measure one cubic centimeter and weigh one gram.
Set includes 1000 cubes in 10 different colors.
This set can be used to teach both metric mass and volume and the connection between them.
The cubes interlock for easier storage.
None noted. The set I have has held up with no damage for years.
This product is available from Learning Resources for $29.99.