TB21 : Freeform pieces come in precision-cut 2 cm increments (2,4,6,8 and 10cm) with large 2cm disks and bridges to support successful building and early math and metric system learning. Diameter of blocks varies. A typical set includes "Y" or forked pieces. Safe, lab tested. Boxed.TB35 : This is a 36 piece set of smooth blocks in a fabric bag. Blocks are precision cut into specific lengths of 2cm, 4cm, 6cm, 8cm and 10cm. Helps with early learning math and metric system.