Coin with Square Hole in Center [solved]

This coin is 25 mm in diameter. The square hole in the center is 7 mm in both directions. The coins weighs 3.82 grams. The characters on the coin are difficult to read. Looking through the selections on this website, it could be of Chinese, Korean, Japanese, or Vietnamese origin. This coin was purchased as part of a "Seven Seas Collection of World Coins" that was packaged in 1975. Any assistance in determining the identity of this coin is greatly appreciated. Thank you!

Hello,

Please try to take more focused pictures, it's also hard to read the characters on the coin when the photo was taken from ten meters away! You also seem to have uploaded photos of only one side of the coin too.

In any case, it's a Korean 1 Mun, with a batch number of "4"; however to find the exact type you can look here:
https://en.numista.com/catalogue/korea-1.html#c_korea6417

Previous camera was not allowing me to zoom without creating a grainy image. Here are some better resolution photos.

Korea "Sang P'yong T'ong Bo", the invariable inscription of their mainline cash coinage. Reverse shows most clearly here, is Military Training Command (mint), "to" (earth) at bottom, furnace #4 at side. Appears badly cast, and then heavily worn.

Thank you for the information you have provided. Any idea as to its year?