Try not double nutting. Try stronger bolt. Make sure there are no special instructions for that bolt like: don't tighten too tight, etc. Is it only one specific place???? (that would be a sure sign). The square hole is to hold the bolt while tightening nut. Why are you double nutting? 3 times in 30 years is not frequent but odd. No others have reported it that I know of. Don't know if it happened on old parts AND on new parts?? On a 3/8 307A, the shear strength is about 4000 lbs!!! The proof load is about 3300 lbs. A quality Gr 5 will not break.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
| 
