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The main problem with this application is the type of material the nuts are being made from, most likely common mild steel. If someone were to use a better material ($) it would eliminate the expansion issue, although I believe the flats should be machined externally (like a 5/8 hex nut) to eliminate the problem entirely.
Rick
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Rick
As you slide down the Banister of Life, may the splinters never be pointing the wrong way 
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