They are made to flex once the proper torque is reached i believe. I didn’t think they were this readily available and inexpensive…
check it out: http://www.torquestick.com/cart/customer/product.php?productid=45&cat=17&page=1
i’ll be ordering mine in the near future.
I would assume that as the metal fatigues with use it weakens… i would think they have a limited service life and thus a replacement interval…