Originally Posted by
Iride01
I'd think it sheared from being too soft a bolt as opposed to too hard and brittle. In this small size it's common to find ungraded bolts and most soft and cheap. You might find some graded bolts in good selection at the auto parts store hanging up on a display rack.
Hmmm, I've never seen "softness" mentioned as an engineering property for bolt materials. Perhaps you seek the property called "strength."