Can be applied at one day of age, but they stay on better if the bird is over 2 weeks of age. Place band in special Jiffy wing band pliers (#893S) and squeeze, band pierces and locks closed all in one motion. Sold in lots of 100 numbered bands. May be customized with your initials, words or numbers at extra cost. Plain aluminum (silver color) are $1.00 per box less than colored.