What do the four hexagonal wooden squares on the gate of an ancient building mean?

This thing is called a door hairpin, which is a structural part used to fix the door leaf. At first, the door facing the door can be fixed with two door nails, and later it evolved into a decorative component, with four in the majority. I have two pictures here to show you its structure and function. The inside of the door bolt is connected with the lintel, which is used to nail the lintel to the upper sill, and the upper end of the door shaft is mounted on the lintel, so that the door can be fixed.

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