I have a saddle somewhat similar to this one. One bolt holding saddle clamp to the seatpost.
Some half a year ago I was riding with no hands and leaned back a bit. Suddenly, I fell down the bike on my back yet later to realize that the bolt simply broke, its head unattached from the threaded shaft. Luckily, I didn't have any serious injury, and neither did bike.
So I replaced the bolt.
Today, same thing happened. But I wasn't even riding hands free, I had one hand on, and was talking on the mobile phone with other. This time I managed to stay on bike and discovered again that the head of the bolt unattached from its shaft.
Now, maybe I put the saddle to far back so I had extra large lever and too much pressure on the screw. However, the flat part of the metal construction is a lot shorter on my saddle than the one here in the picture and I really don't believe I can put it that far even if I want.
Maybe I over tightened the bolt, there was no indication on how much pressure to use, but I was careful, at least the second time.
Do you know what might be the cause for this? Is it possible to over tighten the bolt? Is there something else that might cause this?
PS. Not that it's your business but I weigh 90 kilograms (199 pounds)
PPS. Please save me from the comments "don't ride no hands" and "don't talk on phone while riding". I realize this is somewhat dangerous and I know it increases pressure on the bolt, I wanted to know is there some other thing that might have caused this that didn't occur to me.