Is It Possible to Over-Tighten a Bolt?

Is it possible to over-tighten a bolt? Can over-tightening weaken the bolt? How do I know if the bolt is too tight or too loose?

—Matthew Glass, via email

Yes, you can over-tighten a bolt, but doing so is unlikely. Most bolts come with instructions that the bolt’s maximum torque. The ó-inch
Power Bolt, for example, has a maximum torque of 25-foot pounds. Climbers, however, aren’t apt to study any instruction manual outside of the Kama
Sutra, and prefer to wing it when only their lives are on the line. They are even less likely to purchase, learn to use, and use a torque wrench, the
tool necessary for accurately measuring bolt tightness. Are we then all in danger? The torque necessary to break a ó-inch bolt requires a socket on
at least a 12-inch handle, and a lot of muscle. This situation is unlikely on a cliff, where you’ll have a short wrench that skips off the bolt head
and cheese-graters your knuckles long before you over-tighten the bolt. For the second part of your question, about a bolt being loose: An obviously
loose bolt will move in the hole, and the hanger might spin, although a spinning hanger can also indicate a hole that is too shallow. As a guideline,
when I place a bolt, I wrench it down until it stops turning under normal pressure, i.e. I don’t hammer on the wrench, don’t bounce on it and don’t
apply body weight. A bolt tightened this way should be in the Goldilocks zone for torque: not loose, but not too tight. Next!

This article was published in Rock and Ice issue 233 (April 2016).