The tiny bands are cut with nail scissors from the sheet shown below, according to the size of the bird, and shaped and filed by hand.
The help of some magnification is needed to read the bands of retraps.
Green Violet ear
Purple-throated Mountain Gem
and Fiery-throated Hummingbird
The bills of young hummingbirds show striations ( growth marks)along the edge of the upper mandible. As the hummingbird gets older, the bill gets harder and smoother, and these bill striations disappear. So the percentage of striations on the bill is recorded and used to help age the bird.