Q. Can you please suggest a non destructive/non pin moisture meter to check walnut core moisture, the thickness of walnut would be 10/4 or 60 mm?

A. I do not know of any practical technique for measuring the core MC except for the pin meter or the destructive oven-drying tests. Note that you can use nails instead of pins with the meter and you will get the wettest MC along the length of the pin.

If you are concerned about the needle holes, you might try putting a few drops of water in the hole after you withdraw the needles. As you squished the fibers when you drove the pins, the water will cause the squished fibers to swell back to their original shape and fill the hole almost perfectly.