I am still using original Ariel / (Burman?) bolts and have never had one shear over the past 45 years plus. I drill the heads to lock wire them and don't find the drilling anything of a problem. In fact, in the early years, I have drilled the heads using a hand drill, so they can't be too hard. Even with the lock wire, it is not uncommon for the bolts to work loose but, as I say, I have yet to shear one.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.