Well I use those perdy neon zip ties of course, lol. Hot Pink for Girls, Electric Blue for Boys! (That's just for my keepers... for my sale birds I use yellow and orange, lol). I use the itty bitty ones for the babies, and the normal size for the older birds... like around 6 weeks old. I put em on so they fit loose on the leg to allow for growth, but not loose enough to come off over the foot, that way I only have to snip em off with fingernail clippers every few weeks or so and put new ones on as they grow. Once they reach 10-12 weeks their legs are pretty much full grown and they can wear the same one for 6 months or more unless they come apart and fall off
(Some people worry the birds might get hung up on something with a band like this on their leg, but I've banded both keets and adults like this for years with no one ever getting hung up on anything).

(Some people worry the birds might get hung up on something with a band like this on their leg, but I've banded both keets and adults like this for years with no one ever getting hung up on anything).