Although it is actually a cap of a pipe, I will use a round hole in the board and try using it. It seems like it will fit so as not to rattle with a nail raised slightly. It seems that it will not come off. I think that it is a convenient part even if I use it if there is no problem with the original use method.
I purchased a stainless steel pipe at the home center for setting up the post, but because I do not have a cap, I was looking for a cap because I do not want rain to accumulate in rainy weather. There is no indication of the inside diameter, but I entered a pipe with an outside diameter 38 inside diameter 34 mm. It becomes satisfying because it becomes a cool refreshing post pole which is very refreshing when installed!