In your picture, note that the top has a concave surface and the bottom appears to be flat.

I would suggest you consider some method that would keep the bottom in place. Flat stock as a clamp may not be sufficient to keep the bottom from shifting.

Rather than 1/4 inch, I would opt for a a 5/16 inch bolt. And, I would go with ny-lok nuts rather than tapping.

John Stewart
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