The pieces snap together into a flexible chain to measure length, width and circumference. Pieces come in six colors and include an Activity Guide. Customer Reviews: These linking inchworms are a cute and easy way for children to practice measuring. They are easy to snap together and take apart and the little inchworm on top makes them look a little bit more fun than a regular block. One tub of 72 was enough for my students to use for math workstations with 5 students each working independently.