Approx length is 7-8mm (based that on the photo of the one on the paper, may bot be accurate enough for you). Just a side note on the paper eating - the hole was through the envelope, through the bill (if you fold it the holes align), and the postbox is plastic, not wood.
Just to reiterate this point - the most important thing for me as a home owner is to know what to look out for, and what proactive steps can be taken to minimise the chance of damage. A resource with photo's, pointers, and advice could be really useful.
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