[Jim Sims]

For internal (female) threads of a given size there is about a 3% stripping area advantage of coarse threads over fine threads however I believe the "stronger grip" of the case-savers is due to the fact they have a larger outer diameter and hence are engaging more case material in shear. The coarse thread explanation is at odds with fastener compliance theory and experience: a big coarse stiff steel thread will pass most of the joint load to the first matching thread in the magnesium and can lead to a failure of that magnesium thread. When the first thread fails the load is passed to the second thread and it fails and so on. I strongly suspect that if fine threads were used at the larger diameter of the case-savers the joint would be stronger still as long as the thread size doesn't approach the magnesium grain structure size. Were there any pull tests done to compare the stength of the case-savers versus Time-Certs? Have the case-savers been in service long enough to demonstrate their long term superiority or possible flaws? Cheers, Jim