These 40" (100 cm) fixed Bamboo Circulars are made of Moso bamboo which is the largest and strongest bamboo out of over 1,000 different species. Sizes US3 (3.25 mm) and larger have a nickel-plated, copper join that is glued and crimped to guarantee no separation. The joins are fantastic, the nylon cable is pliable and the tips swivel freely! Needle size is permanently laser imprinted on each circular.