I have 2 Mikimoto clasps from my mother's double strand of AA Mikimoto pearls. She had both strands restrung on a double clasp. I have the original single clasps. My sister got the pearls. I got the clasps. Sigh.
The clasps are marked 750, which is 18K gold.
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Photo quality of your photos does not allow me to see enough detail in the clasp. But to me, the M is the wrong shape. The outer legs angle out, whereas the M on my clasp are vertical. The number is not 750. The back of your clasp is not the same shape, and there are no horizontal bars on the back of your clasp. I can't see enough detail on the face of the clasp to see if the carving is the same, but I suspect they took more trouble with getting the front right.
I took a couple more photos with a US quarter since that is what they are using for scale.
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My clasp looks slightly larger than your clasp.
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I would recommend you talk to Mikimoto. I know they used to use silver clasps originally, but I thought they when they switched to gold, that they used 18K only.
Here's a link to Ruby Lane's Mikimoto pearls. The sellers show the fronts and backs of the different clasps. It's good to look just to compare the different clasps they used over the years.
https://www.rubylane.com/search?q=mikimoto&sb=1