Spiral plastic reusable numbered bands in several colors. The sizes are the number of 1/16" the band's inside diameter is, i.e. size 9 = 9/16" diameter. Size 6 is for young birds (normal size American game chickens or Leghorn size birds) approximately 1-3 months of age, size 7 approx. 2 - 4 months old, size 9 will fit if they out grow a 6 or 7 and also is the size for most hens or small cocks (Puerto Rican / Spanish type cocks) and size 11 is for older stags and cocks that are in the 4.5 to 5.5 pound range, size 12 is for approx. 5.5 to 7 pound cocks.