Sizing a panting stay

[Svinshallah]

The panting stay on my Norseman 447 has broken twice. As built, it was a 1/4" flat tang welded to a piece of 5/8" Taiwanese SS rod at the top. The bottom end had a threaded stud, seemingly from a 1/2" turnbuckle welded to the rod. A turnbuckle was in the bilge. In the first case the bottom weld broke. In the second case, the rod broke where it passed through the cabin sole.

It seems to me that either the rod size is much larger than required, or the 1/2" turnbuckle and clevis pins are much too small. I can't find any information. Any suggestions?