I personally use cable ties, different colours and trimmed-just snip them off and replace when/if necessary. So they are colour coded to tell me what parents they are from. I don't yet have so may that I can't tell them apart anyway though. The rumpless araucana have poultry club leg rings, 16mm I think but they are quite small for LF., 18mm for the cock.
cable ties are easier to use IME! when I first started, I got some wee metal ones of different colours and they were horrible sharp things that were impossible to get off one handed. Spirals were slightly easier and the click together ones are alright on those that have finished growing.