Bird nest box hole/protector

thingiverse

The smaller blue tits need smaller holes to stop the great tits from chasing them out. The great tits on their hand need protection from woodpeckers and squirrels... Mount this protection ring in front of an existing hole to get the right size and protection all at once. The birds do need to be able to read Swedish in order to find the correct nest, but that should not be a problem since they do travel a lot.