This is a waterproof band for the Whoop 4.0 fitness tracker. Please print using flexible TPU with a 75A shore hardness or lower, such as Ninjatek Chinchilla or Colorfabb Varioshore. Harder TPU such as 95A will be uncomfortable on the skin. It hooks onto the original Whoop 4.0 buckle and requires an original Whoop 4.0 band for assembly.