Comment by Peteragain

I did an apprenticeship in metalwork many..many years ago and I seem to recall the zinc is meant to be in compression. If a zinc plug pulled out, it was in shear. Sounds wrong to me. Vincenti: https://en.wikipedia.org/wiki/What_Engineers_Know_and_How_Th... Has a chapter on flush pop rivetting which discussed the loss of this kind of knowing.