Protect your birdhouse's nest guests against unwanted woodpecker attacks with this nest guard! With this metal ring, it will be tough for the woodpecker to try to widen the nest hole to access any eggs and chicks in the nest. The ring is 40 mm and is intended for birdhouses with a 38 mm opening. A very effective protection against woodpeckers. Adapted for blue tit, pine tit, entita etc.